Replying to the salam of a disbeliever

Allah's Messenger ﷺ said: “When the People of the Book (Jews and Christians) greet you with salam, say: ”وعليكم“ (And upon you).”

1. Sahih al-Bukhari, no. (6258), Sahih Muslim, no. (2163), Sunan Abi Dawud, no. (5207), Sunan at-Tirmidhi, no. (3301), Sunan Ibn Majah, no. (3697).