What is the ruling on the prayer of one who doubted the number of prostrations, then based it on certainty and added an extra prostration, then did not perform the prostration of forgetfulness (sujud al-sahw) after the salutation, thinking that it was not required of him?

First: Whoever doubts the number of prostrations, such as doubting whether he performed one prostration or two, should build upon certainty, which is the lesser number. So he considers it one prostration and performs the second, then performs the prostration of forgetfulness before the salaam. Some scholars are of the opinion that if one of the two possibilities is more preponderant in his mind, he should act upon it and perform the prostration of forgetfulness after the salaam.

Second: Whoever forgets to perform the prostration of forgetfulness should perform it if the interval is not long. However, if the interval is long, or he invalidates his ablution, or leaves the mosque, the prostration of forgetfulness is waived for him, and his prayer is valid. An ignorant person in this regard is like one who forgets, and his prayer is valid.