Muwatta Malik #484

Yahya related to me from Malik from Hisham ibn Urwa from his father from A'isha, the wife of the Prophet, may Allah bless him and grant him peace, that al-Harith ibn Hisham asked the Messenger of Allah, may Allah bless him and grant him peace, "How does the revelation come to you?" and the Messenger of Allah, may Allah bless him and grant him peace, said, "Sometimes it comes to me like the ringing of a bell, and that is the hardest for me, and when it leaves me I remember what it has said. And sometimes the angel appears to me in the likeness of a man and talks to me and I remember what he says." A'isha added, "I saw it coming down on him on an intensely cold day, and when it had left him his forehead was dripping with sweat."