Warrad, the scribe of Sayyiduna al-Mughirah (may Allah be pleased with him), said: Sayyiduna al-Mughirah (may Allah be pleased with him) wrote to Mu'awiyah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) used to say after the prayer: "There is no true god except Allah, He is alone, He has no partner; His is the dominion and to Him belongs all praise, and He has power over all things."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18033