Musnad Abu Ya'la al-Mawsili 106:48

Zakariya ibn Yahya narrated to us, Salih ibn Umar narrated to us, Yazid ibn Abi Ziyad narrated to us, from Abd al-Rahman ibn Abi Layla, from al-Bara’ who said: When the Messenger of Allah (may Allah bless him and grant him peace) would begin the prayer, he would raise his hands until he aligned them with his ears. I mentioned that to Adi ibn Thabit, and he said: "I have indeed heard al-Bara’ mention that."