عَنْ عَبْدِ اللَّهِ رَضِيَ اللَّهُ عَنْهُ قَالَ جَاءَ رَجُلٌ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ فَقَالَ أَيُّ الذَّنْبِ أَكْبَرُ قَالَ أَنْ تَجْعَلَ لِلَّهِ نِدًّا وَهُوَ خَلَقَكَ قَالَ ثُمَّ أَيٌّ قَالَ ثُمَّ أَنْ تَقْتُلَ وَلَدَكَ مِنْ أَجْلِ أَنْ يَطْعَمَ مَعَكَ قَالَ ثُمَّ أَيٌّ قَالَ ثُمَّ أَنْ تُزَانِيَ بِحَلِيلَةِ جَارِكَ قَالَ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ تَصْدِيقَ ذَلِكَ فِي كِتَابِهِ {وَالَّذِينَ لَا يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ إِلَى قَوْلِهِ وَمَنْ يَفْعَلْ ذَلِكَ يَلْقَ أَثَامًا} [الفرقان: 68]
It is narrated from Sayyiduna Abdullah (may Allah be pleased with him) that a man came to the Noble Prophet (peace and blessings be upon him) and asked: Which sin is the greatest? The Prophet (peace and blessings be upon him) replied: That you associate a partner with Allah, while He created you. He asked: Then which one? The Prophet (peace and blessings be upon him) replied: Then that you kill your child out of fear that he will eat with you. He asked: Then which one is it? The Prophet (peace and blessings be upon him) replied: Then that you commit adultery with your neighbor’s wife. So Allah Almighty confirmed these matters in His Book with these words: And those who do not call upon any other god along with Allah, nor kill a soul which Allah has forbidden except by right, nor commit adultery—and whoever does this shall meet a severe penalty. (: Surah Al-Furqan: 68)