Sunan an Nasai
1321
Hasan Sahih+2

It was narrated that Wasi' bin Habban said:"I said to Ibn 'Umar: "Tell me about the prayer of the Messenger of Allah (ﷺ); how was it?" He mentioned the takbir and he mentioned: As-salamu 'alaykum wa rahmatullah (peace be upon you and the mercy of Allah) to his right and: As-salamu 'alaykum (peace be upon you) to his left

Hasan SahihAbu Ghuddah
Hasan SahihAl-Albani