Musnad Abu Ya'la al-Mawsili 125:2

'Uqbah ibn Mukram narrated to us, Yunus ibn Bukayr narrated to us, Muhammad ibn 'Ubayd Allah al-Fazari narrated to us, from 'Ata', from Anas: That the Prophet, peace and blessings of Allah be upon him, performed the funeral prayer over his son Ibrahim, and he pronounced the takbir four times over him.