Chapter 1: Revelation
Narrated 'Aisha: (the mother of the faithful believers) Al-Harith bin Hisham asked Allah' s Messenger (ﷺ) "O Allah' s Messenger (ﷺ)! How is the Divine Inspiration revealed to you?" Allah' s Messenger (ﷺ) replied, "Sometimes it is (revealed) like the ringing of a bell, this form of Inspiration is the hardest of all and then this state passes off after I have grasped what is inspired. Sometimes the Angel comes in the form of a man and talks to me and I grasp whatever he says." 'Aisha added: Verily I saw the Prophet (ﷺ) being inspired divinely on a very cold day and noticed the sweat dropping from his forehead (as the Inspiration was over).
Sahih al-Bukhari 2