Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates this statement of the Noble Prophet (peace and blessings be upon him): "Satan comes to a person during his prayer and makes his prayer doubtful for him, to the extent that the person does not know how much he has prayed. So when someone faces such a situation, he should perform the prostration of forgetfulness (sajdah sahw) at the time when he is sitting."