Musnad Ahmad 1237:14

Waki' narrated to us, he said: 'Abd al-Hamid ibn Ja'far narrated to us, from Yazid ibn Abi Habib, from Abu Basrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "We are going out early tomorrow to the Jews, so do not initiate the greeting of peace (salam) to them. If they greet you, then say: 'Wa 'alaykum' (And upon you)."