A man who forgets a prostration of the prayer and remembers it while praying

Al-Hasan said: If a man forgets one of the prostrations of the prayer at the beginning of his prayer and does not remember it until he is in the last rak'ah of his prayer, he should make three prostrations in that rak'ah. If he does not remember it until he has completed his prayer, but has not yet given the salam, he should make one prostration, as long as he has not spoken; and if he has spoken, he should start the prayer afresh.

Ibrahim said: If a man forgets to make a prostration in the prayer, he should make it whenever he remembers it during the prayer.

Mujahid was asked: A man becomes doubtful whether he made a prostration or not, and he is now sitting; what should he do? He said: If you wish, make the prostration, and then, when you have completed the prayer, make the two prostrations of forgetfulness while sitting. And if you wish, do not make it, and make two prostrations while sitting at the end of the prayer.