Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1260 (DarusSalam) ⓘ

It was narrated from 'Abdullah that : The Messenger of Allah offered one of the afternoon prayers with five (rak'ahs), and it was said to him: "Has something been added to the prayer?" He said: 'Why are you asking?' They said: 'You prayed five.' He said: 'I am only human, I forget as you forget, and I remember as you remember.' Then he prostrated twice then ended his prayer.

أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ أَبِي بَكْرٍ النَّهْشَلِيِّ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَسْوَدِ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى إِحْدَى صَلاَتَىِ الْعَشِيِّ خَمْسًا فَقِيلَ لَهُ أَزِيدَ فِي الصَّلاَةِ فَقَالَ ‏"‏ وَمَا ذَاكَ ‏"‏ ‏.‏ قَالُوا صَلَّيْتَ خَمْسًا ‏.‏ قَالَ ‏"‏ إِنَّمَا أَنَا بَشَرٌ أَنْسَى كَمَا تَنْسَوْنَ وَأَذْكُرُ كَمَا تَذْكُرُونَ ‏"‏ ‏.‏ فَسَجَدَ سَجْدَتَيْنِ ثُمَّ انْفَتَلَ ‏.‏