Musannaf Ibn Abi Shayba 27:300

Abu Mu’awiyah narrated to us, from ‘Abd al-‘Aziz ibn Siyah, from Habib ibn Abi Thabit, regarding His saying: "Then Allah sent down His tranquility upon him." He said: Upon Abu Bakr. He said: As for the Prophet, may Allah bless him and grant him peace, the tranquility was upon him before that.