Mishkat al-Masabih 49

ʿAbd Allah ibn Masʿud reported that a man asked, “Messenger of God, which sin is greatest in God’s sight?” He replied, “That you set up a rival to God, though He created you.” The man asked, “Then which?” He replied, “That you kill your child for fear that he will eat with you.” He asked, “Then which?” He replied, “That you commit adultery with your neighbour’s wife.”

Then God, mighty and exalted, revealed words confirming this: “Those who do not call upon another god alongside God, nor kill a soul God has forbidden except with right, nor commit fornication—whoever does that will meet requital.” The passage continues; the Arabic source ends its quotation with “the verse.”