Sahih Bukhari
Dealing with Apostates
Volume: 009 / Book Number: 084 / Hadith Number: 62
Narrated Ibn 'Umar:
Allah's Apostle said, "When the Jews greet anyone of you they say: 'Sam'Alaika (death be upon you); so you should say; 'Wa 'Alaika (and upon you).'"