Sahih Muslim Book 4, Hadith Number 1232.

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

Warrad, the freed slave of Mughira b. Shu’ba, reported: Mughira b. Shu’ba wrote to Mu’awiya (it was Warrad who wrote this letter for him, i.e. Mughira): I heard the Messenger of Allah (may peace be upon him) saying: “When the salutation is pronounced.” and the rest of the Hadith is the same except this that he made no mention of: “He is Potent over everything.”