Narrated 'Abdullah:

I said 'O Allah's Apostle! Which sin is the greatest?" He said, "To set up a rival unto Allah, though He Alone created you." I said, "What next?" He said, "To kill your son lest he should share your food with you." I further asked, "What next?" He said, "To commit illegal sexual intercourse with the wife of your neighbor." And then Allah revealed as proof of the statement of the Prophet: 'Those who invoke not with Allah any other god)................. (to end of verse)...' (25.68)

حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا سُفْيَانُ، عَنْ مَنْصُورٍ، عَنْ أَبِي وَائِلٍ، عَنْ عَمْرِو بْنِ شُرَحْبِيلَ، عَنْ عَبْدِ اللَّهِ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ أَىُّ الذَّنْبِ أَعْظَمُ قَالَ " أَنْ تَجْعَلَ لِلَّهِ نِدًّا وَهْوَ خَلَقَكَ ". ثُمَّ قَالَ أَىُّ قَالَ " أَنْ تَقْتُلَ وَلَدَكَ خَشْيَةَ أَنْ يَأْكُلَ مَعَكَ ". قَالَ ثُمَّ أَىُّ قَالَ " أَنْ تُزَانِيَ حَلِيلَةَ جَارِكَ ". وَأَنْزَلَ اللَّهُ تَصْدِيقَ قَوْلِ النَّبِيِّ ﷺ {وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ}.