Sunan At-Tirmidhi

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