Sahih Muslim 5653
صحيح مسلم#5653SahihAnas reported that the Companions of Allah's Apostle (ﷺ) said to him:The People. of the Book offer us salutations (by saying as-Salamu- 'Alaikum). How should we reciprocate them? Thereupon he said: Say: Wa 'Alaikum (and upon you too)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 39:8