Sahih al-Bukhari 6258
صحيح البخاري#6258SahihNarrated Anas bin Malik:the Prophet (ﷺ) said, "If the people of the Scripture greet you, then you should say (in reply), 'Wa'alaikum (And on you)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 79:32