Oneness, Uniqueness of Allah (Tawheed)

Bukhari :: Book 9 :: Volume 93 :: Hadith 573

Narrated Abu Huraira:

The Prophet said, "When Allah ordains something on the Heaven the angels beat with their wings in obedience to His Statement which sounds like that of a chain dragged over a rock. His Statement: "Until when the fear is banished from their hearts, the Angels say, 'What was it that your Lord said?' 'They reply, '(He has said) the Truth. And He is the Most High, The Great. " (34.23)