"The Messenger of Allah . Verily, Allah, with Him (alone) is the knowledge of the Hour up to His saying: 'Verily, Allah is All-Knower, All-Aware (of things).' Then he said: 'No, by the One who sent Muhammad with the truth, with guidance and glad tidings, I did not know him more than any man among you. That was Jibril, peace be upon you, who came down in the form of Dihyah Al-Kalbi.'"
Sunan an-Nasa'i Book 47, Hadith 7