Sahih al-Bukhari 1226
Book 22: Forgetfulness in Prayer
Arabic
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.
English translation
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
Reference: Sahih al-Bukhari 1226, Book of Forgetfulness in Prayer. English translation by Dr. Muhammad Muhsin Khan.