Abdullah reported: I asked the Messenger of Allah (peace and blessings of Allah be to him):Which sin is the gravest in the eye of Allah? He (the Blessed Messenger) replied: “That you associate a partner with Allah (despite the fact) that He has created you.”He (the reporter) said: I told him (the Blessed Messenger): Verily it is indeed grave. He (the reporter) said: I asked him what the next (gravest sin) was. He (the Blessed Messenger) replied: “That you kill your child out of fear that he shall be joining you in food.” He (the reporter) said: I asked (him) what the next (gravest sin) was. “Then (the next gravest sin) is that you commit adultery with the wife of your neighbour.”
(Sahih Muslim)
This hadīth brings into light three gravest sins. The first is polytheism. Man is created by Allah and it is the height of ingratitude on his part that he should associate partners with his Creator. He has been made the Vicegerent of Godon earth, but he bowsdown before deities who are among Allah’s creations.
The practice of killing children isthe denial of the rububiyah of God. The modern craze for birth control is based on a false concept of God that He is a tyrant.
Adultery in itself is a very grave offence but is most shamefully grave when committed with the wife of a neighbour. A person has every right to expect fellow feeling and security from his neighbour and believe that his trust would not be betrayed.