It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that once someone asked the Prophet (peace and blessings be upon him): "Which sin is the greatest?" The Prophet (peace and blessings be upon him) said: "To associate someone with Allah, especially when it is Allah who created you." The questioner said: "After that, which sin is the greatest?" The Prophet (peace and blessings be upon him) said: "To kill your child out of fear that he will eat with you." The questioner asked: "After that?" He said: "To commit adultery with your neighbor's wife."