Musannaf Ibn Abi Shayba 3:666

Narrated to us Umar ibn Ubayd, from Abu Ishaq, from Abu al-Ahwas, from Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to perform the taslim to his right until the whiteness of his cheek appeared: "As-salamu alaykum wa rahmatullah" (Peace be upon you and the mercy of Allah). And to his left, he did the same.