Sahih al-Bukhari 1226
Sahih al-Bukhari · Book 22: Forgetfulness in Prayer · If one offers five Rak'a (instead of four)
Narrated' `Abdullah:
حَدَّثَنَا أَبُو الْوَلِيدِ ، حَدَّثَنَا شُعْبَةُ ، عَنِ الْحَكَمِ ، عَنْ إِبْرَاهِيمَ ، عَنْ عَلْقَمَةَ ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى الظُّهْرَ خَمْسًا فَقِيلَ لَهُ أَزِيدَ فِي الصَّلاَةِ فَقَالَ " وَمَا ذَاكَ ". قَالَ صَلَّيْتَ خَمْسًا. فَسَجَدَ سَجْدَتَيْنِ بَعْدَ مَا سَلَّمَ.
Once Allah's Messenger (ﷺ) offered five rak`at in the Zuhr prayer, and somebody asked him whether there was some increase in the prayer. Allah's Messenger (ﷺ) said, "What is that?" He said, "You have offered five rak`at." So Allah's Messenger (ﷺ) performed two prostrations of Sahu after Taslim.