Musnad Ahmad 27:1479

'Abd al-Razzaq narrated to us, Sufyan informed us, from 'Abdullah ibn Dinar, from Ibn 'Umar, that the Prophet (peace and blessings of Allah be upon him) said: "When the Jews greet you, they say: 'As-samu 'alaykum' (Death be upon you)." So the Prophet (peace and blessings of Allah be upon him) said: "Then say: 'Wa 'alaykum' (And upon you)."