“God: there is no god but Him, the Ever Living, the Ever Watchful. Neither slumber nor sleep overtakes Him. All that is in the heavens and in the earth belongs to Him. Who is there that can intercede with Him except by His leave? He knows what is before them and what is behind them, but they do not comprehend any of His knowledge except what He wills. His throne extends over the heavens and the earth; it does not weary Him to preserve them both. He is the Most High, the Tremendous.” (Quran, 2:255)
For more:
http://www.whyislam.org/submission/concept-of-god-submission/concept-of-god-in-islam/