Al-Husayn ibn Sa’id from Safwan ibn Yahya from al-’Is ibn al-Qasim, who said: I asked Abu Abdillah عليه السلام 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: "Let him stand, perform the bowing, and prostrate, and then perform the two prostrations of forgetfulness (sujud al-sahw)."