Musannaf Ibn Abi Shayba 3:63

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Ibn Abi Layla, from al-Hakam and ‘Isa, from ‘Abd al-Rahman ibn Abi Layla, from al-Bara’ ibn ‘Azib, that the Prophet (may Allah bless him and grant him peace), when he began the prayer, would raise his hands, then he would not raise them again until he finished.