Sayyiduna Jubayr bin Mut'im (may Allah be pleased with him) narrated: He came regarding the ransom of the captives of Badr. He said: I found the Messenger of Allah (peace and blessings be upon him) reciting in the Maghrib prayer: "Wal-Tur, wa kitabin mastur, fi raqqin manshur" (By the Mount, and by a Book inscribed, on an unrolled parchment). He said: Something like distress came over me from his (peace and blessings be upon him) recitation, and that was the very first thing I heard of the matter of Islam.
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1485