Sahih Bukhari Volume 4, Book 54, Hadith Number 441.

Narated By Ibn Abbas : Allah’s Apostle asked Gabriel, “Why don’t you visit us more often than you do?” Then the following Holy Verse was revealed (in this respect): “And we (angels) descend not but by the order of your Lord. To Him belong what is before us and what is behind us, and what is between those two and your Lord was never forgetful.” (19.64)