Sahih Bukhari
Characteristics of Prayer
Volume: 001 / Book Number: 012 / Hadith Number: 793
Narrated 'Abdullah bin Malik bin Buhaina:
Once Allah's Apostle led us in the Zuhr prayer and got up (after the prostrations of the second Rak'a) although he should have sat (for the Tashah-hud). So at the end of the prayer, he prostrated twice while sitting (prostrations of Sahu).