Narrated `Abdullah: I asked Allah's Messenger (ﷺ) "What is the biggest sin in the sight of Allah?" He said, "To set up rivals unto Allah though He alone created you." I said, "In fact, that is a tremendous sin," and added, "What next?" He said, "To kill your son being afraid that he may share your food with you." I further asked, "What next?" He said, "To commit illegal sexual intercourse with the wife of your neighbor."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ أَبِي وَائِلٍ، عَنْ عَمْرِو بْنِ شُرَحْبِيلَ، عَنْ عَبْدِ اللَّهِ، قَالَ سَأَلْتُ النَّبِيَّ صلى الله عليه وسلم أَىُّ الذَّنْبِ أَعْظَمُ عِنْدَ اللَّهِ قَالَ " أَنْ تَجْعَلَ لِلَّهِ نِدًّا وَهْوَ خَلَقَكَ ". قُلْتُ إِنَّ ذَلِكَ لَعَظِيمٌ. قُلْتُ ثُمَّ أَىّ قَالَ " ثُمَّ أَنْ تَقْتُلَ وَلَدَكَ تَخَافُ أَنْ يَطْعَمَ مَعَكَ ". قُلْتُ ثُمَّ أَىّ قَالَ " ثُمَّ أَنْ تُزَانِيَ بِحَلِيلَةِ جَارِكَ ".
sunnah.com