Musnad Ahmad 1153:1489

Ali ibn Asim narrated to us, from al-Hadhdha’, from Abdullah ibn al-Harith, from Aisha, the Mother of the Believers, that the Messenger of Allah (peace and blessings of Allah be upon him), when he would conclude the prayer with the taslim, would say: "O Allah, You are Peace, and from You is peace. Blessed are You, O Possessor of Majesty and Honor."