Musnad Ahmad 22:9

Ali ibn Ishaq narrated to us, Abdullah ibn al-Mubarak informed us, Layth ibn Sa’d informed us, Abd Rabbih ibn Sa’id narrated to us, from Imran ibn Abi Anas, from Abdullah ibn Nafi’ ibn al-’Amya’, from Rabi’ah ibn al-Harith, from al-Fadl ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The prayer is two by two; you recite the Tashahhud in every two rak'ahs, and you show humility, submissiveness, and destitution. Then you raise your hands,"—he said: "You raise them toward your Lord, with their palms facing your face, saying: 'O Lord, O Lord.'" Whoever does not do that, he said regarding him a severe statement.