The Messenger of Allah ﷺ said, "When one of the Jews greets you, he is really saying, 'Death be upon you,' so reply, 'And upon you.'"
قال رسول الله ﷺ إن اليهود إذا سلم عليكم أحدكم فإنما يقول: السام عليكم، فقل: عليك.
Malik narrated it in "Greetings" (3) from Abdullah bin Dinar, from Abdullah bin Umar, and he mentioned it. Bukhari narrated it in "Seeking Permission" (6257) through Malik's route with the same wording. Muslim narrated it in "Greetings" (2164) through other routes from Abdullah bin Dinar with the same wording.