Hadith 1245 - 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 us not sure about his prayer, then let him estimate what is correct, then let him prostrate twice after he finished his prayer, while he is sitting."

Reference: 1245
English reference: Vol. 2, Book 13, Hadith 1246
In-book reference: Book 13, Hadith 67
Grade: Sahih (Darussalam)
Read this hadith from Darussalam Collection

25) باب التَّحَرِّي

أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ شُعْبَةَ، عَنِ الْحَكَمِ، قَالَ سَمِعْتُ أَبَا وَائِلٍ، يَقُولُ قَالَ عَبْدُ اللَّهِ مَنْ أَوْهَمَ فِي صَلاَتِهِ فَلْيَتَحَرَّ الصَّوَابَ ثُمَّ يَسْجُدْ سَجْدَتَيْنِ بَعْدَ مَا يَفْرُغُ وَهُوَ جَالِسٌ ‏.‏