Ahmad b. Muhammad b. Yahya al-`Attar narrated to us. He said: My father narrated to us from Ahmad b. Muhammad b. `Isa from al-Husayn b. Sa`id from `Ali b. Ja`far from Muhammad b. `Umar al-Jarjani. He said: Al-Sadiq Ja`far b. Muhammad said:

In the first ever congregational prayer, the Messenger of Allah (s) prayed and Amir al-Mu’minin `Ali b. Abi Talib prayed with him when Abu Talib passed by him with Ja`far [b. Abi Talib]. He said: “O my son! Pray with your cousin.” When the Messenger of Allah (s) sensed him, he took a step forward from the two of them [to lead them both in prayer]. Abu Talib left happily, saying: Surely, `Ali and Ja`far are my two trustees When time and calamity are overwhelming, By Allah, I will not fail the Prophet, nor will my son whatsoever, Do not fail him, and support your cousin, He is like a maternal brother and a father to me. He said: That was the first congregational prayer that gathered that day.