Sahih Muslim Book 4, Hadith Number 768.

Chapter : The desirability of raising the hands apposite the shoulders at the time of beginning the prayer and at the time of bowing and at the time of returning to the erect position after bowing.

Abu Salama reported that Abu Huraira recited takbir in prayer on all occasions of rising and kneeling. We said: O Abu Huraira, what is this takbir? He said: Verily it is the prayer of the Messenger of Allah (may peace be upon him).