Sahih al-Bukhari 1226
Narrated' `Abdullah:
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.
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.‏