Musannaf Ibn Abi Shayba 3:3664

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, who said: I said to Ibrahim, "I hear a man while I am praying saying, 'Indeed, Allah and His angels send blessings upon the Prophet.' Should I send blessings upon him?" He said, "Yes, if you wish."