A hadith narrated by Abu Saeed Khudri رضي الله عنه says that the Prophet ﷺ taught that when a person has doubt in prayer, he should act on what he is sure about, complete the prayer, and then perform two prostrations. The hadith shows that these extra actions become voluntary if the prayer was already complete.

Islamic scholars used this hadith as evidence that Sujood Sahw is a Sunnah act. It is not obligatory. If a mistake happens in prayer and Sujood Sahw is not performed, the prayer is still correct. This fatwa clearly states that missing Sujood Sahw does not invalidate the prayer according to Islamic ruling.