Ameer al-Momineen (a.s) said: “Do not initiate greeting to the people of the Book, but whenever they greet you just say “Alaykum” meaning “be upon you”.”
عن أمير المؤمنين (عليه السلام) قال
لا تبدؤوا أهل الكتاب بالسلام، وإذا سلموا فقولوا " عليكم ".
Similar narrations
Al-Kāfi #2202“Amir al-Mu’minin, Ali ibn abu Talib (a.s.) has said, ‘Do not initiate the offering of the greeting of peace to people of the Book, but if...