Musnad Ahmad

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) would begin the obligatory prayer after the takbeer, he would say "Allahu Akbar" and raise his hands to the level of his shoulders. After completing the recitation, when he (peace be upon him) would go into bowing (ruku'), he would do the same. When rising from ruku', he would do the same. While sitting, during any posture, he (peace be upon him) would not raise his hands. However, when he would stand up after performing both prostrations, he would say the takbeer while raising his hands.