Musnad Ahmad 33:916

Rawh narrated to us, Muhammad ibn Hafsah narrated to us, Ibn Shihab narrated to us, from Abu Salamah ibn Abd al-Rahman, from Jabir ibn Abdullah, who said: The revelation was withheld from the Messenger of Allah (peace and blessings of Allah 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 returning from Hira, "I heard a sound from above me. I raised my head, and behold, the one who had come to me at Hira was above me on a chair." He said: "When I saw him, I fell to the ground. When I recovered, I went to my family quickly and said: 'Wrap me up, wrap me up.' Then Gabriel came to me and said: 'O you (Muhammad) enveloped in garments, arise and warn! And your Lord (Allah) magnify! And your garments purify! And keep away from idols!'"