Musnad Ahmad 498:1

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, he said: I heard ‘Abd Rabbih ibn Sa‘id narrating from Anas ibn Abi Anas, from ‘Abdullah ibn Nafi‘ ibn al-‘Amya’, from ‘Abdullah ibn al-Harith, from al-Muttalib, from the Prophet, peace and blessings of Allah be upon him, who said: "The prayer is two by two, and you recite the tashahhud in every two rak‘ahs, and you show distress, and you show humility, and you raise your hands, and you say: 'O Allah, O Allah.' Whoever does not do that, it is deficient." And Hajjaj said: "And you raise your hands."