Hadith 1246 - 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 'Abdullah said: "Whoever has doubt, or is not sure, let him estimate what is correct, then let him prostrate twice."

Reference: 1246
English reference: Vol. 2, Book 13, Hadith 1247
In-book reference: Book 13, Hadith 68
Grade: Sahih (Darussalam)
Read this hadith from Darussalam Collection

25) باب التَّحَرِّي

أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ مِسْعَرٍ، عَنِ الْحَكَمِ، عَنْ أَبِي وَائِلٍ، عَنْ عَبْدِ اللَّهِ، قَالَ مَنْ شَكَّ أَوْ أَوْهَمَ فَلْيَتَحَرَّ الصَّوَابَ ثُمَّ لْيَسْجُدْ سَجْدَتَيْنِ ‏.‏