مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3826
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: I saw the Messenger of Allah (ﷺ) saying the salam to his right, as-salamu 'alaikum wa rahmatullah, until the whiteness of his right check could be seen, and to his left in like manner.
Musnad Ahmad 3849Its isnad is saheeh]