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

From him, from Abdur-Rahman ibn Abi Najran from Safwan from al-‘Ayyas, who said: I asked Abu Abdillah عليه السلام, peace be upon him, about a man who forgot a rak‘ah from his prayer until he finished it, then remembered that he had not bowed. Imam عليه السلام said: "He should stand, perform the bowing, and then perform two prostrations."