Musnad Ahmad 3713

It was narrated that ‘Abdullah (رضي الله عنه) said: I saw the Messenger of Allah (ﷺ) saying takbeer every time he raised or lowered his head (in prayer), when standing and sitting, and he said the salam to his right and to his left, as-salamu ‘alaikum warahmatullah, as-salamu ‘alaikum warahmatullah, until I could see the whiteness of his check and I saw Abu Bakr and 'Umar doing likewise.