'Abdullah ibn 'Umar said that the Messenger of Allah, may Allah
bless him and grant him peace, said, "When one of the Jews greets you and
says, 'Poison be upon you (as-samu 'alaykum),' say, 'And on you.'"
Ibn 'Abbas said, "Return the greeting to whomever it is, Jew,
Christian, or Magian. That is because Allah says, 'When you are greeted
with a greeting, greet with one better than it or return it.' (4:86)"