Musnad Ahmad 602:1

Yazid ibn Harun narrated to us, Muhammad ibn Ishaq informed us, and Ibn Abi ‘Adi, from Muhammad ibn Ishaq, Ibn Abi Habib narrated to me—and Yazid said: from Ibn Abi Habib—from Marthad ibn ‘Abdullah al-Yazani, from Abu ‘Abd al-Rahman al-Juhani, he said: The Messenger of Allah (ﷺ) said to us: "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)."