Musnad Ahmad 26:337

'Abd al-Razzaq narrated to us, al-Thawri narrated to us, from Jabir, from Abu al-Duha, from Masruq, from 'Abdullah, who said: Among what I have not forgotten of the Messenger of Allah (may Allah bless him and grant him peace) is that he used to say the taslim to his right: "Peace be upon you and the mercy of Allah," until the whiteness of his cheek could be seen. And to his left: "Peace be upon you and the mercy of Allah," until the whiteness of his cheek could be seen as well.