Lady Aisha Siddiqa (may Allah be pleased with her) narrates: Harith bin Hisham asked the Prophet Muhammad (peace be upon him), he said: O Messenger of Allah! How does revelation come to you? The Prophet Muhammad (peace be upon him) replied: Sometimes it comes to me with the sound of a bell, and this is the most intense for me. When this state leaves me, I remember what the angel has said.
Sometimes the angel comes to me in the form of a man, and talks to me, so I remember what he says.
Lady Aisha (may Allah be pleased with her) narrates: I have seen the Prophet Muhammad (peace be upon him), once on a very cold day revelation descended upon him, and when this state left him, sweat was pouring from his blessed forehead.