Allah's Messenger (ﷺ) said, "When the Jews greet you, they usually say, 'As-Samu 'alaikum (Death be on you),' so you should say (in reply to them), 'Wa'alaikum (And on you).
Sahih al-Bukhari Book 79, Hadith 31
← Previous Hadith A group of Jews came to Allah's Messenger (ﷺ) and said, "As-samu 'Alaika " (Death be on you), and I understood it and said to them, "Alaikum AsSamu wa-l-la'na (Death and curse be on you)." Allah's Apostle said, "Be calm! O `Aisha, for Allah loves that one should be kind and lenient in all matters." I said. "O Allah's Messenger (ﷺ)! Haven't you heard what they have said?" Allah's Messenger (ﷺ) said, "I have (already) said (to them), 'Alaikum (upon you).' "

Sahih al-Bukhari Book 79, Hadith 30 Next Hadith → the Prophet (ﷺ) said, "If the people of the Scripture greet you, then you should say (in reply), 'Wa'alaikum (And on you).' "

Sahih al-Bukhari Book 79, Hadith 32