Musnad Ahmad 26:299

Hashim and Husayn—the meaning being the same—said: Isra’il and Abu Ahmad narrated to us. Isra’il narrated to me, from Abu Ishaq, from Abu al-Ahwas and al-Aswad ibn Yazid, from ‘Abdullah, who said: I saw the Messenger of Allah (peace and blessings of Allah be upon him) saying the taslim to his right: "As-salamu ‘alaykum wa rahmatullah" (Peace be upon you and the mercy of Allah), until the whiteness of his right cheek appeared, and to his left in the same manner.