Musannaf Ibn Abi Shayba 3:720

Hushaym narrated to us, from Abu Harun, from Abu Sa’id al-Khudri, who said: I heard the Prophet, may Allah bless him and grant him peace, more than once saying at the end of his prayer, when he was finishing: "Exalted is your Lord, the Lord of might, above what they describe. And peace be upon the messengers. And praise be to Allah, Lord of the worlds."