Yahya bin Abu Kathir reported,

I asked Abu Salama bin Abdul-Rahman about the first portion of the Quran to be revealed.He said, "O you who is wrapped in garments" [Muddaththir 74:1].I said, "But people say it was 'Recite in the name of your Lord who created' [Alaq 96:1]."Abu Salama replied, "I asked Jabir bin Abdullah about this and said to him the same thing you have said to me. Jabir answered, 'I will tell you only what the Messenger of Allah ﷺ told us. He said, "I had been in seclusion at Hira. When my retreat was completed, I came down, and a voice called out to me. I looked to my right and saw nothing. I looked to my left and saw nothing. I looked in front of me and saw nothing. I looked behind me and saw nothing. Then I raised my head and saw something. I went to Khadijah and said, 'Wrap me up, and pour cold water over me.' So they wrapped me up and poured cold water over me. Then was revealed, 'O you who is wrapped in garments, arise and warn, and magnify your Lord'"' [Muddaththir 74:1–3]."

عن يحيى بن أبي كثير، قال

سألت أبا سلمة بن عبد الرحمن عن أول ما نزل من القرآن قال: {يا أيها المدثر}. قلت: يقولون {اقرأ باسم ربك الذي خلق}؟ فقال أبو سلمة: سألت جابر بن عبد الله عن ذلك، وقلت له: مثل الذي قلت. فقال جابر: لا أحدثك إلا ما حدثنا رسول الله ﷺ قال: جاورت بحراء، فلما قضيت جواري هبطت فنوديت، فنظرت عن يميني فلم أر شيئا، ونظرت عن شمالي فلم أر شيئا، ونظرت أمامي فلم أر شيئا، ونظرت خلفي فلم أر شيئا، فرفعت رأسي فرأيت شيئا، فأتيت خديجة فقلت: دثروني، وصبوا علي ماء باردا. قال: فدثروني وصبوا علي ماء باردا. قال: فنزلت: {يا أيها المدثر قم فأنذر وربك فكبر} [سورة المدثر: ١- ٣].