Narrated Anas bin Malik: A Jew passed by Allah's Apostle and said, "As-Samu 'Alaika." Allah's Apostle said in reply, "We 'Alaika." Allah's Apostle then said to his companions, "Do you know what he (the Jew) has said? He said, 'As-Samu 'Alaika.'" They said, "O Allah's Apostle! Shall we kill him?" The Prophet, said, "No. When the people of the Book greet you, say: 'Wa 'Alaikum.'"

Narrated `Aisha: A group of Jews asked permission to visit the Prophet (and when they were admitted) they said, "As- Samu 'Alaika (Death be upon you)." I said (to them), "But death and the curse of Allah be upon you!" The Prophet said, "O `Aisha! Allah is kind and lenient and likes that one should be kind and lenient in all matters." I said, "Haven't you heard what they said?" He said, "I said (to them), 'Wa 'Alaikum (and upon you).

Narrated Ibn `Umar: Allah's Apostle said, "When the Jews greet anyone of you they say: 'Sam'Alaika (death be upon you); so you should say; 'Wa 'Alaika (and upon you).'"