Sahih Al Bukhari Hadith Number 800

Narrated Thabit: Anas used to demonstrate to us the prayer of the Prophet (peace be upon him) and while demonstrating, he used to raise his head from bowing and stand so long that we would say that he had forgotten (the prostration).

10  Call to Prayers (Adhaan)
Hadith number 800
Volume no 1
Chapter: 127 (To stand Straight with calmness on raising the head from bowing)