Musannaf Ibn Abi Shayba 3:668

Waki’ narrated to us, from Hurayth, from al-Sha’bi, from al-Bara’, that the Prophet (peace and blessings of Allah be upon him) used to perform the taslim to his right and to his left: "Assalamu alaikum wa rahmatullah" (Peace be upon you and the mercy of Allah), until the whiteness of his cheek could be seen.