Mukhtasar Bukhari

Narrated from Umm al-Mu'mineen Aisha Siddiqa (may Allah be pleased with her): Harith bin Hisham asked the Messenger of Allah (peace and blessings of Allah be upon him), "O Messenger of Allah! How does revelation come to you?" The Messenger of Allah (peace and blessings of Allah be upon him) replied: "Sometimes it comes to me like the ringing of a bell, and (among all the states of revelation) this state is the hardest upon me. Then this state departs from me, and I have grasped what the angel has said. And sometimes the angel comes to me in the form of a man and speaks to me, and I remember what he says." Umm al-Mu'mineen Aisha (may Allah be pleased with her) says: Indeed, I have seen revelation descending upon the Prophet (peace and blessings of Allah be upon him) on a very cold day, and when the process ended, I saw that sweat was dripping from his (blessed) forehead.