HOW TO GREET THE PEOPLE OF THE BOOK H 880 "When the people of the Book greet you, you should respond with, 'And upon you.'" R 880 Bukhari and Muslim with a chain up to Anas who related that the Prophet, praise and peace be upon him, said this.
867- وعن أنسٍ رضي الله عنه ، قَالَ : قَالَ رسول الله صلى الله عليه وآله وسلم : "إِذَا سَلَّمَ عَلَيْكُمْ أهْلُ الكِتَابِ فَقُولُوا : وَعَلَيْكُمْ" متفقٌ عَلَيْهِ .