Musannaf Ibn Abi Shayba 36:24

Muhammad ibn Abi Hafsa narrated to us, from al-Zuhri, from Abu Salamah, from Jabir, who said: The revelation was withheld from the Prophet, peace and blessings be upon him, at the beginning of his affair, and seclusion was made beloved to him. So he began to seclude himself in Hira. While he was coming down from Hira, he said: "Suddenly, I heard a sound above me. I raised my head, and behold, there was something upon a throne. When I saw it, I fell to the ground in fear. I went to my family quickly and said, 'Wrap me up! Wrap me up!' Then Gabriel came to me and began to say: 'O you who are wrapped in garments, arise and warn, and your Lord magnify, and your garments purify, and the idols avoid.'"