Musnad Ahmad 33:1097

'Affan narrated to us, Aban al-'Attar narrated to us, Yahya ibn Abi Kathir narrated to us, he said: I asked Abu Salamah ibn 'Abd al-Rahman: Which of the Qur'an was revealed first? He said: "O you who are wrapped in garments" (Al-Muddaththir: 1). I said: Indeed, I was informed that the first surah revealed was: "Read in the name of your Lord who created" (Al-'Alaq: 1). Jabir said: I will not narrate to you except as the Messenger of Allah, peace and blessings of Allah be upon him, narrated to us. He said: "I was in retreat at Hira, and when I completed my retreat, I descended and reached the middle of the valley. I was called out, so I looked in front of me, behind me, to my right, and to my left, but I did not see anything. Then I was called out again, so I looked in front of me, behind me, to my right, and to my left, but I did not see anything. Then I looked above me, and there he was, sitting on a throne between the heaven and the earth. I was struck with fear of him, so I came to Khadijah's house and said: 'Wrap me up, and pour cold water over me.'" He said: Then there was revealed to me: "O you who are wrapped in garments, arise and warn, and your Lord glorify" (Al-Muddaththir: 2-3).