Musnad Abu Ya'la al-Mawsili 32:1

Abu Khaythama narrated to us, Ibn Numayr narrated to us, from Muhammad ibn Ishaq, from Yazid ibn Abi Habib, from Marthad ibn Abdullah al-Yazani, from Abu Abd al-Rahman al-Juhani, who said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "I am riding tomorrow to the Jews, so do not initiate the greeting of peace (salam) to them. And if they greet you, then say: 'Wa alaykum' (And upon you)."