Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

And from him, from Ahmad ibn al-Hasan ibn Ali ibn Faddal, from Amr ibn Sa‘id, from Musaddiq ibn Sadaqah, from Ammar al-Sabati: Abu Abdillah عليه السلام (was asked) regarding the man upon whom frequent doubt occurs in prayer, so he doubts in the bowing and does not know whether he bowed or not, and he doubts in the prostration and does not know whether he prostrated or not. Imam عليه السلام said: "He should neither prostrate nor bow, and he should continue in his prayer until he is certain with certainty." And (Imam عليه السلام was asked) regarding the man who forgets a prostration and remembers it after he has stood and bowed. Imam عليه السلام said: "He should continue in his prayer and not prostrate until he completes it with the salam. Then when he has given the salam, he should perform a prostration like that which he missed." I asked: “What if he does not remember except after that?” Imam عليه السلام said: "He should make up what he missed whenever he remembers it."