Warrad relates that al-Mughirah bin Shu'bah (may Allah be pleased with him) wrote a letter to Mu'awiyah (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) completed his prayer he would say, and he mentioned the like of it in identical words.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3017