Sahih Ibn Khuzaymah

Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that when the Messenger of Allah (peace and blessings be upon him) would begin the prayer, he would say « اللهُ أَكْبَرُ », then raise both his hands up to the level of his shoulders, and when he would bow (ruku‘), he would do the same (raise the hands), and when he would prostrate, he would do the same, and when he would raise his head from prostration, he would not raise his hands, and when he would stand up after the (tashahhud of) two rak‘ahs, he would do the same (raise the hands).