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.'"
Sahi Bukhari, Volume 9, Book 84, Number 60 ------------------------------------------------------------------------------ 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). Sahi Bukhari, Volume 9, Book 84, Number 61 ------------------------------------------------------------------------------ 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).'" Sahi Bukhari, Volume 9, Book 84, Number 62