Sahih Muslim, Chapter: Prayers (Kitab Al-Salat)

The Messenger of Allah (may peace be upon him) raised his hands apposite his ears at the time of reciting the takbir (i. e. at the time of beginning the prayer) and then again raised his hands apposite the ears at the time of bowing and when he lifted his head after bowing he said: Allah listened to him who praised Him, and did like it (raised his hands up to the ears).