Fortress of the Muslim
Hisn al-Muslim 227
Arabic hadith text
إذَا سَلَّمَ عَلَيْكُمْ أَهْلُ الْكِتَابِ فَقُولُوا: وَعَلَيْكُمْ
Translation
When the People of the Book greet you, say: “And upon you.”