Yahya reported,

I asked Abu Salama which part of the Quran was revealed first.He replied, "You who are wrapped in your cloak" [Muddaththir 74:1].I said, "I was told it was 'Recite in the name of your Lord who created' [Alaq 96:1]."Abu Salama then said, "I asked Jabir bin Abdullah which part of the Quran was revealed first, and he answered, 'You who are wrapped in your cloak' [Muddaththir 74:1]."I said to him, "I was told it was 'Recite in the name of your Lord who created' [Alaq 96:1]."Jabir replied, "I will tell you only what the Messenger of Allah ﷺ said. The Messenger of Allah ﷺ said, 'I had been secluded in Hira, and when my period of seclusion ended, I came down and made my way into the valley. I was called. I looked in front of me, behind me, to my right, and to my left, and there he was, seated on a throne between the heavens and the earth. I went to Khadijah and said, Wrap me up and pour cold water over me. Then there was revealed to me, "You who are wrapped in your cloak, arise and warn, and magnify your Lord" [Muddaththir 74:1–3].'"

Bukhari 4924

Sahih

حدثنا إسحاق بن منصور حدثنا عبد الصمد حدثنا حرب حدثنا

يحيى قال

سألت أبا سلمة أي القرآن أنزل أول فقال {يا أيها المدثر} فقلت أنبئت أنه {اقرأ باسم ربك الذي خلق} فقال أبو سلمة سألت جابر بن عبد الله أي القرآن أنزل أول فقال {يا أيها المدثر} فقلت أنبئت أنه {اقرأ باسم ربك الذي خلق} فقال لا أخبرك إلا بما قال رسول الله ﷺ قال رسول الله ﷺ جاورت في حراء فلما قضيت جواري هبطت فاستبطنت الوادي فنوديت فنظرت أمامي وخلفي وعن يميني وعن شمالي فإذا هو جالس على كرسي بين السماء والأرض فأتيت خديجة فقلت دثروني وصبوا علي ماء باردا وأنزل علي {يا أيها المدثر قم فأنذر وربك فكبر}

البخاري 4924صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Tafsir
Chapter
His saying, "And your Lord, glorify Him"
Numbering
Darussalam 4924
Bukhari 4924