Sunan Ibn Majah 3697
سنن ابن ماجه#3697SahihIt was narrated that Anas bin Malik said "the Messenger of Allah(ﷺ) said":"When any of the People of the Book greets you with Salam (peace), then say, Wa 'alaikum(and also upon you)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih
In-book reference: 33:41