Musnad Abu Ya'la al-Mawsili 115:312

Ubayd Allah narrated to us, Khalid narrated to us, Sa'id narrated to us, from Qatadah, from Anas ibn Malik, that he mentioned that a Jew passed by the Messenger of Allah (may Allah bless him and grant him peace) while he was with his companions—or he said: while his companions were with him—and he greeted him. He (the Prophet) said: "Do you know what he said?" They said: "No." He said: "Bring him back to me." He said: "I said: 'Sam 'alaykum' (Death be upon you)." He said: "Yes." The Messenger of Allah (may Allah bless him and grant him peace) said: "If the People of the Book greet you, then say: 'Wa 'alaykum' (And upon you)."