Yahya bin Abu Kathir reported,

I asked Abu Salama bin Abdul-Rahman which part of the Quran was revealed first. He said, "Ya ayyuha al-Muddaththir," and he mentioned the hadith, except that he said, "When I had completed my period of seclusion, I came down and made my way into the heart of the valley, and I was called." He also mentioned, "I looked above me, and there he was, seated upon a throne between the heavens and the earth. I was terrified by him and went to Khadijah's house, where I said, 'Cover me up.'" Then he mentioned the rest of the hadith.

Ahmad 14288

Sahih

حدثنا عفان أخبرنا أبان العطار حدثنا

يحيى بن أبي كثير قال

سألت أبا سلمة بن عبد الرحمن أي القرآن أنزل أول فقال يا أيها المدثر فذكر الحديث إلا أنه قال فلما قضيت جواري نزلت فاستبطنت بطن الوادي فنوديت فذكر أيضا قال فنظرت فوقي فإذا هو قاعد على عرش بين السماء والأرض فجئثت منه فأتيت منزل خديجة فقلت دثروني فذكر الحديث

أحمد 14288صحيح
Contents
Reference
Commentary
Ayat
Collection
Musnad Ahmad
Book
Jabir bin Abdullah
Numbering
Darussalam 14288
Ahmad 14288