Prostration of forgetfulness:
They are two prostrations which the one performs prayer may do to make up for whatever decrease or addition made inattentively in one’s prayer. It is to be performed when one inattentively performs something additional during prayer, when one inattentively misses something integral in prayer, or when one is uncertain whether he has performed something additional or missed some integral part in prayer.
One is to do them before Tasleem if there is a decrease in the prayer such as forgetting to do Tasbeeh of bowing or prostration or being uncertain whether he has performed something additional, or missed something in prayer.
One is to do them after Tasleem if there is an increase such as additional bowing, prostration, standing, sitting or being uncertain whether he has performed something additional, or missed something in prayer, or being uncertain whether he has performed something three or four Rak‘ahs, then he knows that he performed only three, then he has to perform another one and do the prostration of forgetfulness after Tasleem.
As for the one who forgets several matters in prayer, it is sufficient for him to do only two prostrations. If he has to prostrate for forgetfulness before and after Tasleem, he has to prostrate only before Tasleem.