Narrated Ibn 'Umar: That the Messenger of Allah (ﷺ) said: "Indeed when a Jew gives Salam to one of you, then he is only saying: 'As-Samu 'Alaikum' (Death be upon you) so say: "Alaik (And upon you).'" [Abu 'Eisa said:] This Hadith is Hasan Sahih

English translation · Jami' at-Tirmidhi