Sahih Muslim Book 4, Hadith Number 1230.

Chapter : Desirability of seeking refuge from the torment of the grave.

Mughira b. Shu’ba wrote to Mu’awiya: When the Messenger of Allah (may peace be upon him) finished the prayer and pronounced salutation he uttered (this supplication): “There is no god but Allah. He is alone, Who has no partner. To Him belongs the sovereignty and to Him praise is due and He is Potent over everything. O Allah! no one can withhold what Thou givest, or give what Thou withholdest, and the riches cannot avail a wealthy person with Thee.”