Musnad Abu Ya'la al-Mawsili 106:23

Muhammad ibn Abd al-Rahman ibn Sahm al-Antaki narrated to us, Abu Ishaq al-Fazari narrated to us, from Abu Ishaq al-Shaybani, that Muharib ibn Dithar narrated to him, he said: I heard Abdullah ibn Yazid saying on the pulpit: Al-Bara ibn Azib narrated to us that they used to pray with the Messenger of Allah, may Allah bless him and grant him peace. When he would bow, they would bow. And when he would raise his head from bowing and say, "Allah hears those who praise Him," we would not cease standing until we saw that he had placed [his forehead on the ground].