Authentic Supplication Number 109.
It is reported by way of the Messenger of Allah that he said: “Whoever makes tasbeeh after each salat 33 times, tahmeed 33 times, takbeer 33 times, and completes a hundred by saying: La ‘ilaha ‘illa ‘allahu wahdahu la shareeka lahu, lahul mulku wa lahul hamdu, wa huwa `ala kulli shay’in qadeerun (130), his sins would be forgiven even if they were as plentiful as the foam of the sea.
(130) There is no ‘ilsah except Allah alone, no associate does He have. His is the Kingdom, to Him is All-Praise, and He is well able to do all things.
Reported by Muslim and is #92 in The Authentic of Good Sayings.