Chapter on the Rulings on Forgetfulness (Ahkam al-Sahw)

Muhammad ibn Mas‘ud from Ja‘far ibn Ahmad, who said: Ali ibn al-Hasan and Ali ibn Muhammad narrated to me by al-‘Ubaydi from Yunus from al-‘Ala’ from Muhammad ibn Muslim from one of the two (Imams عليه السلام): He was asked about a man who joined the Imam (of prayer) in prayer after the Imam (of prayer) had already completed one rak‘ah. When the Imam (of prayer) finished, the man left with the people, then remembered that he had missed a rak‘ah. He said: “He should repeat one rak‘ah, it is permissible for him to do so as long as he has not turned his face away from the qiblah. But if he has turned his face away, then he must begin the prayer anew from the start.”