Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that the Noble Prophet (peace and blessings be upon him) said: When the Jews greet you, they say "As-Saam Alaikum" (death be upon you) instead of "As-Salaam Alaikum" (peace be upon you), so you should also reply with "Wa Alaikum" (and upon you).
Hadith Referenceالفتح الربانی / كتاب السلام والاستئذان وآداب أخرى / 8278
Hadith Gradingمحدثین:صحیح
Hadith Takhrij«أخرجه البخاري: 6928، ومسلم: 2164 ، (انظر مسند أحمد ترقيم الرسالة: 4563 ترقیم بيت الأفكار الدولية: 4563»
Brief Explanation
Benefits: … The meaning of "as-samu ‘alaykum" is: may destruction and death befall you.