Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with this chain of narration, it is narrated from Umm al-Mu’minin Sayyida Aisha (may Allah be pleased with her) that Sayyiduna Harith bin Hisham (may Allah be pleased with him) asked the Messenger of Allah (peace and blessings be upon him): O Messenger of Allah! How does revelation come to you? The Messenger of Allah (peace and blessings be upon him) replied: “Sometimes it comes like the ringing of a bell, and this is hard upon me. Then when it ends, I remember what was revealed. And sometimes the angel comes to me in the form of a man and speaks to me, and I remember what he says.” Sayyida Aisha (may Allah be pleased with her) said: I have seen revelation descending upon you on a very cold day, and when it ended, sweat would be pouring from your forehead.