(25) باب التَّحَرِّي
It was narrated that 'Abdullah said:
"Whoever has doubt, or is not sure, let him estimate what is correct, then let him prostrate twice."
Reference: Sunan an-Nasa'i 1246
In-book reference: Book 13, Hadith 68
English translation: Vol. 2, Book 13, Hadith 1247