(25) باب التَّحَرِّي
It was narrated that Ibrahim said:
"They used to say: 'If one is not sure of what he estimates is correct, then prostrate twice.'" (RU)
Reference (RU): Sunan an-Nasa'i 1247 (RU)
In-book reference (RU): Book 13, Hadith 69 (RU)
English translation (RU): Vol. 2, Book 13, Hadith 1248 (RU)