It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them) that he said: The Messenger of Allah (peace and blessings be upon him) said: "When any of the Jews greets you with Salam, he says: «السام علیک» (death be upon you), so you should also reply with «وعلیک» (death be upon you)."
Hadith Referenceالادب المفرد / كتاب أهل الكتاب / 1106
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه البخاري ، كتاب الاستئذان : 6257 و مسلم : 2164 و أبوداؤد : 5206 و الترمذي : 1603 و النسائي فى الكبرىٰ : 10138»