Musannaf Ibn Abi Shayba 3:709

Abu Mu'awiyah narrated to us, from Awsajah ibn al-Rummah, from Ibn Abi al-Hudhayl, from Ibn Mas'ud, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) would say the taslim, he would not sit except for the duration of what he would say: "O Allah, You are Peace, and from You is peace. Blessed are You, O Possessor of Majesty and Honor."