Musnad Ahmad 26:622

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Jabir, from Abu al-Duha, from Masruq, from 'Abdullah, from the Messenger of Allah (peace and blessings of Allah be upon him), that he "used to say the taslim to his right and to his left, until I could see the whiteness of his face." And I have not forgotten thereafter, among what I have forgotten: "Peace be upon you and the mercy of Allah, peace be upon you and the mercy of Allah."