It was narrated that Mughirah bin Shu’bah said:“The Messenger of Allah (ﷺ) said: ‘If anyone of you stands after two Rak’ah, if he has not yet stood up fully, let him sit down again, but if he has stood up fully, then let him not sit down, and let him perform two prostrations for forgetfulness (Sahw).’”

English translation · Sunan Ibn Majah