It is narrated from Hazrat Anas (may Allah be pleased with him) that once a man from the People of the Book came to the court of the Prophet and, greeting the Prophet (peace be upon him), said, "As-Saam Alaikum." Hearing this, Hazrat Umar (may Allah be pleased with him) said, "O Messenger of Allah (peace be upon him)! Shall I not strike off his neck?" The Prophet (peace be upon him) said, "No, but when the People of the Book greet you, you should only reply with 'Wa Alaikum.'"