Hadith 1247 - The Book of Forgetfulness (In Prayer) - Sunan An-Nasa'i - سنن النسائي - Collection of Actions, Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم) - Kutub as-Sittah

13. The Book of Forgetfulness (In Prayer) - كتاب السهو

25) Chapter: Estimating (what is most likely the case)

It was narrated that Ibrahim said: "They used to say: 'If one is not sure of what he estimates is correct, then prostrate twice.'"

Reference: 1247
English reference: Vol. 2, Book 13, Hadith 1248
In-book reference: Book 13, Hadith 69
Grade: Sahih (Darussalam)
Read this hadith from Darussalam Collection

25) باب التَّحَرِّي

أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنِ ابْنِ عَوْنٍ، عَنْ إِبْرَاهِيمَ، قَالَ كَانُوا يَقُولُونَ إِذَا أَوْهَمَ يَتَحَرَّى الصَّوَابَ ثُمَّ يَسْجُدُ سَجْدَتَيْنِ ‏.‏