A Humiliation for the Shaytan – Sajda Sahu

“When one of you doubts about his prayer and does not know whether he prayed three or four, let him resolve his doubt and act upon what he is more certain of. Then prostrate two prostrations of forgetfulness before tasleem. If he prayed an odd number, then it will complete it evenly for him; and if he prayed four, then they are a humiliation for the Shaytan” [Sahih Muslim]