Sunan An-Nasa'i

It was narrated from 'Abdullah that:The Prophet (ﷺ) said: ""It is as if I can see the whiteness of his cheek, saying to his right: As-salamu 'alaykum wa rahmatullah (peace be upon you and the mercy of Allah) and to his left: As-salamu 'alaykum wa rahmatullah (peace be upon you and the mercy of Allah)."" (Sahih)