Musnad Ahmad 498:6

Hajjaj ibn Muhammad narrated to us, he said: Shu'bah informed me, from 'Abd Rabbih ibn Sa'id, from 'Imran ibn Abi Anas, from the people of Egypt, from 'Abdullah ibn Nafi', from 'Abdullah ibn al-Harith, from al-Muttalib, that the Prophet, peace and blessings of Allah be upon him, said: "The prayer is two by two, and you recite the Tashahhud and perform the Taslim 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, then it is deficient."