His (Imam Reza as ) debate with the Catholic

al-Fadl b. Sahl went in a hurry to the Imām, peace be on him, and said to him: "May I be your ransom, your cousin (i.e. al-Ma'mūn) is waiting for you. The people has gathered. What is your view of going to him?"
The Imām answered him that he was ready to attend (the session) and that he was going to al-Ma'mūn. He went out (walking) with solemnity toward which faces were humble. He remembered Allah and came in to al-Ma'mūn. The session was attended by the Tālibiyyin, the Hāshimites, the military commanders, Muslim and non-Muslim scholars. When the Imām came, al-Ma'mūn and all those who were in the session stood up for him, received him with honor and magnification. The Imām sat while the people were still standing in order to show respect for him. A-Ma'mūn ordered them to sit and they sat down. All the people in the session kept silent as a sign of respect for the Imām, and then al-Ma'mūn turned to the Catholic Archbishop and said to him: "Catholic, this is my cousin 'Ali b. Mūsā b. Ja'far. He is on of the children of F`ātima, daughter of our Prophet, may Allah bless him and his family, and of 'Ali b. Abū Tālib, peace be on him. I would like you to debate with him on theology, argue with him, and show justice toward him.
"Commander of the faithful, how can I argue with a man who argue with me through a Book which we have denied and a Prophet whom I do not believe?" asked the Catholic.
The Catholic thought that the Imām, peace be on him, would produce evidence in support of his beliefs through some verses of the Holy Qur'ān or through some words of the Messenger, may Allah bless him and his family. As he had no faith in the Qur'ānic verses and the Prophetic traditions, he asked the Imām to give proof of his beliefs from their own Books, and the Imām answered him saying: "Christian, if I give proof from your Gospel, will you admit it?"
"Yes," retorted the Catholic, "By Allah, I will admit it. Can l repel what the Bible speaks about?
"Question (me) whatever you desire and hear (my) answers," declared the Imām.
Q1: "What is your view of the Prophethood of 'Īsā (Jesus Christ) and his Book? Do you deny anything of them?"
Ans. 1: "I admit the Prophethood of 'Īsā (Jesus Christ) and his Book, of what he brought good news to his community, and the disciples admitted it. He who does not admit the Prophethood of Mohammed and His Book and does not bring good news of them to his community denies the Prophethood of 'Īsā."
"Aren't precepts proved through two just witnesses?" asked the Catholic.
"Yes," replied the Imām.
"Therefore, name two witnesses from other than the people of your religion and from among those whom the Christians do not deny, that they might (confirm) the Prophethood of Mohammed. And ask us for the like of that from among other than the people of our religion," demanded the Catholic.
The Imām believed his statement, for he brought justice, saying: "Now, you have brought justice. Do you not accept from me the just one who was given preference (over the others) by al-Masih b. Maryam (Jesus, son of Mary)?"
"Who is the just one? Name him for me," asked the Catholic.
"What is your view of Yohannā al-Daylami?" asked the Imām.
"Bravo! Bravo!" retorted the Catholic, "You have mentioned the most lovable of the people to al-Masih."
Imām al-Ridā, the Prophet's grandson, asked him: "I challenge you to swear (by Allah), does the Bible say that Yohannā says: Verily al-Masih has told me of the religion of Mohammed, the Arab, given me good news of him, he will be (a prophet) after him, so I   (Yohanna al-Daylami) gave good news of him to the disciples and they believed him."
The Catholic was unable to deny the Imām's statement, but he said: "Yohannā did not name him for us, that we may recognize him."
The Imām asked him: "If we bring you someone who recites the Bible and recites to you Mohammed's name, his Household, and his community, then will you believe him?"
"A sound suggestion," the Catholic answered.
The Imām turned to Nestus, the Roman, and asked Him: "Have you memorized the third Book of the Bible?"
"I have thoroughly memorized it," was the answer.
The Imām, peace be on him, addressed the Catholic, saying: "Don't you recite the Bible?"
"Yes," he said.
The Imām said: "Therefore (I will) recite to you (some verses from) the third Book. If Mohammed, may Allah bless him and his family, his Household, and his community have been mentioned in it, then bear witness to me? If they have not been mentioned wherein, then do not bear witness to me."     
The Imām recited to him some verses from the third Book. When he reached the reference to the Prophet, may Allah bless him and his family, he turned to the Catholic and asked him: "I challenge you to swear by al-Masih and his mother, did you know that I had knowledge of the Bible?"
"Yes," came the answer.
The Imām recited to him some verses from the third Book concerning the reference to the Prophet, his Household, and his community. Then he asked him: "What is your view? This is the statement of 'Īsā b. Maryam. If you deny what the Bible says, then you will deny Mūsā and 'Īsā. If you deny them, then it is obligatory (on people) to kill you, for you have denied your Lord, your Prophet, and your Book."
The Catholic said: "I do not deny the clear things in the Bible; rather I admit them."
The Imām turned to those who were present and asked them to remind the Catholic of his own words, and then he said to the Catholic: "Catholic, question me whatever you desire."
Q2: "Tell me about the disciples of 'Īsā b. Maryam: How many were they? (Tell me) about the scholars of the Bible: How many were they?" the Catholic asked.
Ans. 2: "You have found the expert! As for (the number of) the disciples, they were twelve men. The best and the most learned of them was loqā. As for (the number of) the scholars of the Christians, it was three men: Yohnnā, the greatest-Yāhi-, Yohannā (Baqriqisiya), and Yohannā al-Daylami (Bazikhār), who had the reference to the Prophet, may Allah bless him and his family, and his Household; it is he who gave good news to the community of 'Īsā and the children of Isrā'il of him (the Prophet)."
The Imām added, saying: "By Allah, we believe in 'Īsā who believed in Mohammed, may Allah bless him and his family. We have nothing against 'Īsā except his weakness and the paucity of his fasting and prayer."
When the Catholic heard the last words of the Imām's statement, he shouted: "By Allah, you have corrupted your knowledge! Your affair has become weak! I thought that you were the most learned of the Muslims!"
The Imām faced him calmly, asking: "Why?"
The Catholic lost his mind, so he began saying: "Because of your statement (which is) that 'Īsā was weak with little fasting and praying, (while) 'Īsā never broke fasting by day and never slept by night. He always fasted by day and prayed by night."
The Imām got ready to disprove the Christian belief which said that al-Masih was a god other than Allah and was served! He asked the Catholic: "For whom did he (al-Masih) fast and pray?"
The Catholic did not answer, not knowing what to say. So the Imām  turned to him, saying : "I want to ask you a question."
"Ask," said the Catholic, "I will answer you if I have knowledge of it."
"Did you not deny that 'Īsā gave life to the dead with Allah's permission?" asked the Imām.
"I had denied that before," the Catholic answered, "he who gives life to the dead, heals the blind and the leprous is a lord worthy of being served."
The Imām disproved his statement, saying: "Indeed al-Yasa' did just as 'Īsā, peace be on him, did: he walked on the water, gave life to the dead, healed the blind and the leprous. Why did his community not adopt him as a lord? Why did not anyone serve him (as a god) other than Allah? He gave life to thirty-five men sixty years after their death. Catholic, you find in the Torah that these (men) were among the youths of the children of Isrā'il whom Bukht Nasr (Nebuchadnezzar) chose from among the children of Isrā'il when he invaded Jerusalem, that he took them and headed for Babylon, and that Allah, the Great and Almighty, dispatched al-Yasa' for them and he gave life to them. This (statement) is in the Torah. None denies it except an unbeliever."
The Catholic admired the Imām's knowledge of their Books, and then he said: "We have heard of it and recognized it."
The Imām turned to a Jew who was in the session and asked him to recite some verses of the Torah and he recited them, and there was in them a reference to some prophets. Then the Imām turned to the Catholic and asked him: "Were these (prophets) before 'Īsa or was he before them?"
"Rather they were before him," was the answer.
The Imām began reciting to them some miracles of his grandfather, the greatest Prophet, the last of the prophets, saying: "Quraysh gathered around Allah's Messenger, may Allah bless him and his family, and asked him to give life to their dead. He sent with them 'Ali b. Abū Tālib and said to him: 'Go to the cemetery and call out at the top of you voice to the people about whom they have asked: So-and-so, so-and-so, Mohammed Allah's Apostle, may Allah bless him and his family, say to you: Rise with the permission of Allah, the Great and Almighty! They rose and dusted off their heads. Quraysh walked toward them and asked them about their affairs, and then they told them that Mohammed was appointed as a prophet. They (the people who rose from the dead) said: 'We would that we knew him and believed in him!' He (the Prophet) healed the blind, the leprous, and the mad. The beasts, the birds, the jinn, and Satan spoke to him, but we did not adopt him as a lord other than Allah. We do not deny the favor of any of these (prophets). If you have adopted 'Īsā as a lord, then it is permissible for you to adopt al-Yasa' and Hizqal as two lords, for they did just as 'Īsā b. Maryam did such as giving life to the dead. Then a group of the children of Isrā'il left their own homeland in thousands out of fear of death of plague. Allah made them die within one hour. The people of the village fenced them, and they remained wherein until their bones became decayed. One of the prophets of the children of Isrā'il passed by them; he was amazed when he saw their many decayed bones. Allah revealed to him: 'Would you like (Me) to bring them to life and you warn them?'
" 'Yes,' was the answer.
"Allah revealed to him that he should call them out, and he said: 'Decayed bones, rise with Allah's permission.' All of them rose and dusted off their heads. Then Ibrāhim, Allah's bosom friend, took the birds, cut them into pieces, and put each piece on a mountain. He called them out and they came toward him walking. Then Mūsā b. 'Umrān and his seventy companions whom he chose. They went with him to the mountain and said to him: 'You have seen Allah, then make us see Him.'
" 'I have not seen Him,' he said to them.
"They said: 'We will not believe in you until we see Allah manifestly. The thunderbolt overtook them, and all of them burnt. Only Mūsā remained (alive).'
"He (Mūsā) said: 'My Lord! I chose seventy men from among the children of Isrā'il and brought them (to the mountain). Shall I return by myself? How shall my people believe what I will tell them about? If only You willed and perished them along with me before! Shall you perish us due to what the foolish did?
"So Allah, the Great and Almighty, gave life to them after their death. You cannot deny all these things which I have mentioned to you, for the Torah, the Bible, the Zabūr (David's Psalms) the Furqān (Qur'ān) have mentioned them. If all those who gave life to the dead, healed the blind, the leprous, and the mad were adopted as lords other than Allah, than you adopt them as lords. What is your view, Christian?"
The Imām criticized the Christians for their adopting al-Sayyid al-Masih as a lord other than Allah, for he gave life to the dead, healed the blind and the leprous, while such miracles happened through the master of the prophets, the Messenger, may Allah bless him and his family, and through some great prophets, but they were not adopted and served as lords other than Allah, the Most High.After the Catholic Archbishop had heard these brilliant words of the Imām, he addressed him, saying: "My view agrees with yours, and there is no god but Allah."
The Imām turned to the High Rabbi and said to him: "Turn to me; I want to ask you about the ten verses which were sent down to Mūsā b. 'Umrān. Have you found written in the Torah the news of Mohammed, may Allah bless him and his family, and his community, (which says): When the last community and the followers of the Rider of the Camel (who) glorify the Lord very, very (much), (with) a new glorification in the new churches (he meant the mosques), then let the children of Isrā'il flee toward them and their dominion, that their hearts may be tranquil, for there will in there hands swords with which they will take vengeance on the unbelieving communities in the regions of the earth. In this manner it has been written in the Torah?"
The Rabbi was amazed and began saying: "Yes, we have found that (written) in this manner."
The Imām, peace be on him, turned to the Catholic and asked him: "What about your knowledge of the Book of Sha'yā?"
"I know it letter for letter," was the answer.
The Imām addressed the Catholic and the Rabbi and said to them: "Do you know that this (statement) is of his speech: O People, I have seen the picture of the Rider of the Donkey. He was wearing the gowns of light. And I have seen that the light of the Rider of the camel is like that of the moon."
They began saying: "Sha'yā did say that!"
The Imām turned to the Catholic and asked him: "Did you know that 'Īsā said: 'I am going to my Lord and your Lord, and the Paraclete is coming who shall testify to my truth just as I testified for him, and he shall explain everything to you, and he shall be the one to expose all the sins of nations, and he shall be the one to smash the pillar of unbelief.'?"
The Catholic became amazed and said: "We admit all what you have just quoted of the Bible."
Then the Imām made him confess that through the Bible, saying: "Have you found that established in the Bible?"
"Yes," came the answer.
"O Catholic, could you tell me about the first Bible, how you lost then found it, and who put your existing Bible together?" asked the Imām.
The Catholic said at random: "We did not lose the Bible except for one single day then we found it fresh; Yohannā (John) and Matti (Matthew) brought it back to us."
The Imām answered him, saying: "How little your knowledge of the Bible and its scholars is! If such is your claim, then why do you dispute with each other about the Bible? Rather, controversy has always revolved around the Bible which is in your hands today. Had it been the same as the first one, you would not have thus dispute (with one another) about it, but I shall inform you of such controversy myself: Be informed that when the first Bible was lost, the Christians gathered around their scholars and said to them: ''Īsā b. Maryam (Jesus son of Mary) has been killed, and we do not know where the Bible is. You are the scholars; so, what do you have with you?'
"Aluqā (Luke), Marqānūs (Mark), and Yohannā (John) said to them: 'We have learned the Bible by heart; so, do not grieve in its regard, and do not forsake the churches, for we shall recite to you one Gospel after another on each Sunday till we put it all together.'"
The Imām added, saying: "Aluqā (Luke), Marqānūs (Mark), Yohannā (John), and Matti (Matthew) put this Bible of yours after you had lost the first (original) one. These four men were students of the early (disciples); are you aware of that?"
The Catholic admired the Imām and confessed to him that he had no knowledge of that, saying: "This I did not know and now I have learned from you things with which I was familiar and to which my heart testifies to be the truth. I have, therefore, gained a better understanding."
The Imām, peace be on him, turned to al-Ma'mūn and those who were present from among his family and others than them. He said to them: "Bear witness to what he has just said."
"We testify," they said.
The Imām addressed the Catholic, saying: "I challenge you to swear by the son and his mother whether you know if Matti (Matthew) had said concerning the lineage of 'Īsā : 'The Messiah is Dāwud (David) son of Ibrāhim (Abraham) son of Ishāq (Isaac) son of Ya'qūb (Jacob) son of Yahūd (Yehuda) son of Khadrun, and that Marqānus (Mark) said about the lineage of 'Īsā that he was the word of Allah which he placed in the human body, so it became human, and that Alūqā (Luke) said that 'Īsā b. Maryam (Jesus son of Mary) and his mother were humans of flesh and blood, so the Holy Spirit entered into them.' Then you testify that 'Īsā had himself said the following about his creation: 'I will tell you the truth: None ascends the heavens except him who descends therefrom except the Rider of the Camel, the seal of the prophets, for he shall ascend to the heavens then shall he descend.' What do you say about that?"
The Catholic admitted what they said about the Messiah and what the Messiah said concerning his creation. He said: "This is the speech of 'Īsā, and we do not deny it."
The Imām said to him: "If so, what do you say about the testimony of Alūqā (Luke), Marqānūs (Mark), and Matti (Matthew) with regard to 'Īsā and what they had attributed to him?"
"They lied about him," was the answer.
The Imām turned to the leaders and the scholars who were present in his session and said to them: "People, has he not (a moment ago) testified to their truthfulness and said that they were the scholars of the Bible and what they said is the truth?"
Defeat appeared on the Catholic's face, and he asked the Imām not to question him, saying: "Scholar of the Muslims, I would like you to excuse me from discussing these men."
The Imām excused him, and then he said to him: "Question me whatever you desire."
The Catholic admired the Imām's knowledge, which was a natural extension to that of his grandfather, the master of all  creatures, Mohammed, may Allah bless him and his family. Then he said to the Imām with submission and admiration: "Let someone other than me ask you. By Allah, I did not think that there was a scholar like you among the Muslims."
The Catholic bowed his head, and the session shook with saying: "There is no god but Allah! Allah is greater!" Al-Ma'mūn and the others came to know that Allah had given the   Imām to this community as a gift just as  He had given his grandfathers to it and supplied them with abundant knowledge.

Reference :The life of Imām'Ali Bin Mūsā al-Ridā