Musnad Ahmad 658:174

Yahya ibn Adam narrated to us, Abu Bakr ibn Ayyash and Ammar ibn Ruzayq narrated to us, from Abu Ishaq, from Abd al-Rahman ibn Awsajah, from al-Bara ibn Azib, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah and His angels send blessings upon the first rows."