Sunan an-Nasa'i #1251 · The Book of Forgetfulness (In Prayer)

Sunan an-Nasa'iIt was narrated from 'Abdullah bin Ja'far that
Sunan an-Nasa'i · Book 13 · The Book of Forgetfulness (In Prayer)
Sunan an-Nasa'i · كتاب 13 · كتاب السهو
The Messenger of Allah (ﷺ) said: "Whoever has doubt during his prayer, let him prostrate twice." (One of the narrators) Hajjaj said: "After he has said the taslim." (Another of them) Rawh said: "While he is sitting
أَخْبَرَنَا هَارُونُ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا حَجَّاجٌ، وَرَوْحٌ، - هُوَ ابْنُ عُبَادَةَ - عَنِ ابْنِ جُرَيْجٍ، قَالَ أَخْبَرَنِي عَبْدُ اللَّهِ بْنُ مُسَافِعٍ، أَنَّ مُصْعَبَ بْنَ شَيْبَةَ، أَخْبَرَهُ عَنْ عُتْبَةَ بْنِ مُحَمَّدِ بْنِ الْحَارِثِ، عَنْ عَبْدِ اللَّهِ بْنِ جَعْفَرٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ مَنْ شَكَّ فِي صَلاَتِهِ فَلْيَسْجُدْ سَجْدَتَيْنِ ‏"‏ ‏.‏ قَالَ حَجَّاجٌ ‏"‏ بَعْدَ مَا يُسَلِّمُ ‏"‏ ‏.‏ وَقَالَ رَوْحٌ ‏"‏ وَهُوَ جَالِسٌ ‏"‏ ‏.‏
Reference : Sunan an-Nasa'i 1251In-book reference : Book 13, Hadith 73