1254An NasaiSahih (Darussalam)أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنِ ابْنِ عَوْنٍ، عَنْ إِبْرَاهِيمَ، قَالَ كَانُوا يَقُولُونَ إِذَا أَوْهَمَ يَتَحَرَّى الصَّوَابَ ثُمَّ يَسْجُدُ سَجْدَتَيْنِ .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: Sunan an-Nasa'i 1247 In-book : Book 13, Hadith 69 English translation : Vol. 2, Book 13, Hadith 1248