It is narrated in Kitab Al-Irshad by Shaykh Al-Mufeed(a.r) that Ali b.Jafar said: God gave Abul Hasan Al-Reza(a.s) victory when his brothers and uncles treated him unjustly.[Then he gave a long account until he came to:] (i.e Ali b.Jafar) arose and seized the hand of Abu Jafar Muhammad b. Ali Al-Reza and I said to him: “I testiy that before God,the Mighty and High,you are Imam”
Imam Al-Reza(a.s) wept and said: “Uncle, did you not hear my father saying:The Apostle(s.a.w.a) said to my father (i.e Ali ibne Abi Talib):The son of the best of the Nubian maid-servants will be among hsi descendants (He will be) pursued,exiled,deprived of his father. His grandson will be the Imam who goes into occultation.It will be said that he has died or had been killed or any such excuse.”
“True, may I be your ransom” I said.