(24) باب إِتْمَامِ الْمُصَلِّي عَلَى مَا ذَكَرَ إِذَا شَكَّ
It was narrated from Abu Sa'eed Al-Khudri that:
The Prophet (ﷺ) said: "If one of you does not know whether he prayed three or four (rak'ahs), let him pray a rak'ah then prostrate twice after that when he is sitting. Then if he prayed five (rak'ahs), they (the two prostrations) will make his prayer even-numbered, and if he had prayed four, they will annoy and humiliate the shaitan." (ID)
Reference (ID): Sunan an-Nasa'i 1239 (ID)
In-book reference (ID): Book 13, Hadith 61 (ID)
English translation (ID): Vol. 2, Book 13, Hadith 1240 (ID)