Musnad Ahmad 1237:13

Hassan narrated to us, Ibn Lahi'ah narrated to us, he said: Yazid ibn Abi Habib narrated to us, from Abu al-Khayr, he said: I heard Abu Basrah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "We are going 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)."