Ibraheem al-Karkhi visited Imam Ja'far b. Muhammed (al-Sadiq), peace be on him. While he was sitting with the Imam, Abu al-Hasan Musa came. Ibraheem rose for him and Abu 'Abd Allah said to him: "Ibraheem, he is your leader after me. Some people will perish through him, and some others will be happy through him. May Allah curse those who will kill him and double chastisement against their souls. Allah will bring forth from his backbone the best of the people of the earth of his time, the namesake of his grandfather and inheritor of his knowledge. The tyrant who belongs to the children of so-and-so will kill him after unique miracles out of envy of him, but Allah will attains His purpose though the polytheists may averse." By him he meant Muhammed al-Mahdi, may Allah bring about his early reappearance, the namesake of the Prophet and the one similar to him in destroying oppression and putting an end to the oppressive.
He talked about his son Allah had gifted with grace and dignity, saying: "Allah will bring forth from his backbone twelve rightly-guided ones. He will distinguished them by his dignity and place them in the abode of His Holiness; he who follows the twelve one from among them is like him who draws his sword before Allah's Apostle to defend him."
When Imam al-Sadiq, peace be on him, reached these words, some Umayyad hirelings broke into his house, and he, peace be on him, stopped his talk. Ibraheem wanted him to complete it but he did not do that; so he left Yethrib (Medina) for his homeland. In the following year he had the honor of visiting the Imam while he felt burning desire for hearing the rest of his speech. The Imam, peace be on him, understood that and said: "Ibraheem, he will remove distress from his Shi'ites after long straits and tribulation, impatience and fear; so blessed is he who lives during his time." Then he said to him: "That is enough for you, Ibraheem."
Ibraheem was pleased with this speech of the Imam and said: "I have never returned with a thing more delightful and happier to my heart than this (speech)." Bihar al-Anwar, vol. 11, 235.