Sunan an Nasai
1083
Sahih+2

It was narrated that Abdullah bin Mas'ud said:"The Messenger of Allah (ﷺ) used to say the takbir every time he went down and came up, and he would say the Salam to his right and his left. And Abu Bakr and 'Umar used to do likewise

SahihAbu Ghuddah
SahihAl-Albani