Abdullah reported: I asked the Messenger of Allah ﷺ: Which sin is the gravest in the eye of Allah? He (the Holy 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 Holy Messenger): Verily it is indeed grave. He (the reporter) said: I asked him what the next (gravest sin) was. He (the Holy 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.”
This hadīth brings into light three gravest sins. The first and foremost is polytheism. Here the Blessed Messenger argues that it is the height of ingratitude on man’s part that he should associate partners with the Creator. This act also lowers his dignity and status.
The practice of killing children is denial of God’s attribute of nourishing. The modern craze for birth control is based on a false concept of God that He is a tyrant and is playing havoc with humanity in the sense that the resources He has created to maintain humanity are far meagre as compared with their ever-increasing numbers. But experience has demonstrated absolute untenability of this assumption.
That adultery with a neighbour’s wife is one of the gravest sins shows how concerned about the dignity of neighbours the Messenger ﷺ was.