It was narrated that ‘Abdullah (رضي الله عنه) said:

I saw the Messenger of Allah (ﷺ) saying takbeer with every bowing and prostration, every time he raised or lowered his head (in prayer), and I saw Abu Bakr and 'Umar (doing likewise), and they said the salam to their right and to their left, assalamu ‘alaikum wa rahmatullah.