Musannaf Ibn Abi Shayba 3:6288

Abu al-Ahwas narrated to us, from Abu Ya'fur, from Abu al-Salt, from Abu Aqrab al-Asadi, who said: We came to Ibn Mas'ud in his house and found him above the house. We heard him say before he descended, "Allah and His Messenger have spoken the truth." We said to him, "We heard you say before you descended, 'Allah and His Messenger have spoken the truth.'" He said, "Indeed, the Night of Decree (Laylat al-Qadr) is in the seven [nights] of the latter half. That is because the sun rises on that day white, having no rays." So I looked at the sun and saw it just as he had described, so I said, "Allahu Akbar" (Allah is the Greatest).