We do not descend except by the Command of your Lord

And we (angels) descend not except by the Command of your Lord (O Muhammad). To Him belongs what is before us and what is behind us, and what is between those two, and your Lord is never forgetful,

[Qur'aan 19:64]

Narrated Ibn `Abbas:

The Prophet (sallallaahu alayhi wa sallam) said to Gabriel, "What prevents you from visiting us more often than you visit us now?" So there was revealed:-- 'And we (angels) descend not but by the command of your Lord. To Him belongs what is before us and what is behind us...'[Qur'aan 19.64]

Sahih al-Bukhari Hadiith No. 3218