Once his tutor Abu Yasir recommended that he attend the lessons in theology by Ali B. Isa al-Rummani, so as to gain deeper insight into the subject. Sheikh excused himself by saying that he was not acquainted with al-Rummani, and therefore needed an introduction. Abu Yasir gave him a letter and also arranged for someone to go with him to al-Rummani.
Sheikh al-Mufid says, I entered his class, and was impressed by the great number of students. So I sat at the end of the crowd, managing to creep forward as some members of the assembly left. Then I saw one man enter, saying: "(O Master), there is someone at the door who insists on being admitted to your presence. He is from Basrah." The master said: "Is he a man of any erudition?"
The servant said: "I do not know, but he seems very keen to be let in." The Master relented, and the man from Basrah entered. The Master welcomed him respectfully, and they had a long conversation between them. Then he asked the Master, Ali b. Isa: "How do you view al-Ghadeer and al-Ghar (the event of the cave in which Abu Bakr accompanied the Prophet during Hijrah)?"
Ali b. Isa replied that "the report of al-Ghar was a recognised event, while al-Ghadeer was just a narrative. And a narrative is not as mandatory as a recognised event." The man from Basrah then left without making any reply.
Al Mufid says: Then I came forward and said: "O Sheikh, I have a question." He said: "Ask." Then I asked: "What do you say about the one who fights a just Imam?" He said: "Such a person would be an infidel." Then, after a pause, he rectified himself and said: "He would be a transgressor."
I asked: "What do you say about Amirul Momineen Ali b. Abi Talib, peace be upon him?" He said: "I believe he was an Imam." So I asked: "Then what do you say about the day of Jamal and Talha and al-Zubair?" He retorted that both of them had repented. I said: "The battle of Jamal is a recognised event, while their repentance is a mere narrative."
Upon hearing this, he said: "Were you present when the man from Basrah put his question?" I said "yes." He said: "Well, a narrative compares a narrative, and a recognised event compares a recognised event." Then turning to me again, he asked: "What is your name and who is your tutor?" I said: " I am known as Ibn al-Muallim, and my tutor is Abu-Abdillah, al-Jual." He said: "Stay where you are."
Then he entered his room and came out with a letter, instructing me to hand over to my tutor. When I gave the letter to my tutor, he read it and then laughed. "What transpired between you in his class? He has asked me to confer upon you the title of al-Mufid." I related to him the story, so he smiled.
The above incident has been recorded by Mirza Muhammad Baqir al-Khwansari in Rawdhat-ul-Jannaat (vol. 6 p. 159), quoting from al-Saraa-er of Ibn ldrees and from Majmua'h Warraam. But Ibn Shahr Ashob in hisMa'alimul Ulamaa says that the title 'al-Mufid' was given to Sheikh al-Mufid, by our twelfth Imam, al-Hujjah, Sahebuzzaman, may his advent be soon.