Sahih al-Bukhari 65:4
Narrated `Abdullah:
I asked the Prophet, "What is the greatest sin in the Sight of Allah?" He said, "That you set up a rival unto Allah though He Alone created you." I said, "That is indeed a great sin." Then asked, "What is next?" He said, "To kill your son lest he should share your food with you." I asked, "What is next?" He said, "To commit illegal sexual intercourse with the wife of your neighbor."
Reference
Sahih al-Bukhari 65:4
In-book reference
Book 65, Hadith 4
Arabic Text
حَدَّثَنِي عُثْمَانُ بْنُ أَبِي شَيْبَةَ، 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 أَىُّ قَالَ " وَأَنْ تَقْتُلَ وَلَدَكَ تَخَافُ أَنْ يَطْعَمَ مَعَكَ ". قُلْتُ ثُمَّ أَىُّ قَالَ " أَنْ تُزَانِيَ حَلِيلَةَ جَارِكَ ".