Fath al-Rabbani

Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) narrates from the Messenger of Allah (peace and blessings be upon him) that when he (peace and blessings be upon him) would stand for the obligatory prayer, he would say Allahu Akbar and raise his hands up to the level of his shoulders. Then, when he completed his recitation and intended to bow (ruku‘), he would raise his hands in the same manner, and when he raised his head from ruku‘, he would do the same. He (peace and blessings be upon him) would not raise his hands in any part of the prayer while sitting, and when he stood up after two rak‘ahs (for the third rak‘ah), he would raise his hands in the same way and say Allahu Akbar.