Sahih al-Bukhari 404
Narrated `Abdullah:
"Once the Prophet (ﷺ) offered five rak`at in Zuhr prayer. He was asked, "Is there an increase in the 
prayer?" The Prophet (ﷺ) said, "And what is it?" They said, "You have prayed five rak`at.' So he bent his 
legs and performed two prostrations (of Sahu).
حَدَّثَنَا مُسَدَّدٌ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ شُعْبَةَ، عَنِ الْحَكَمِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ صَلَّى النَّبِيُّ صلى الله عليه وسلم الظُّهْرَ خَمْسًا فَقَالُوا أَزِيدَ فِي الصَّلاَةِ قَالَ ‏
"‏ وَمَا ذَاكَ ‏"‏‏.‏ قَالُوا صَلَّيْتَ خَمْسًا‏.‏ فَثَنَى رِجْلَيْهِ وَسَجَدَ سَجْدَتَيْنِ‏.‏