Sahih Muslim Book - 1, Hadith - 258

حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ جَمِيعًا عَنْ جَرِيرٍ قَالَ عُثْمَانُ حَدَّثَنَا جَرِيرٌ عَنْ الْأَعْمَشِ عَنْ أَبِي وَائِلٍ عَنْ عَمْرِو بْنِ شُرَحْبِيلَ قَالَ قَالَ عَبْدُ اللَّهِ قَالَ رَجُلٌ يَا رَسُولَ اللَّهِ أَيُّ الذَّنْبِ أَكْبَرُ عِنْدَ اللَّهِ قَالَ أَنْ تَدْعُوَ لِلَّهِ نِدًّا وَهُوَ خَلَقَكَ قَالَ ثُمَّ أَيٌّ قَالَ أَنْ تَقْتُلَ وَلَدَكَ مَخَافَةَ أَنْ يَطْعَمَ مَعَكَ قَالَ ثُمَّ أَيٌّ قَالَ أَنْ تُزَانِيَ حَلِيلَةَ جَارِكَ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ تَصْدِيقَهَا { وَالَّذِينَ لَا يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ وَلَا يَقْتُلُونَ النَّفْسَ الَّتِي حَرَّمَ اللَّهُ إِلَّا بِالْحَقِّ وَلَا يَزْنُونَ وَمَنْ يَفْعَلْ ذَلِكَ يَلْقَ أَثَامًا }.

It was narrated that 'Amr bin Shurahbil said: "Abdullah said: 'A man said: "O Messenger of Allah, which sin is worst before Allah?" He said: "Ascribing a partner to Allah when He (is the One Who) has created you." He said: "Then what?" He said: "Killing your child for fear that he may share your food." He said: "Then what?" He said: "Committing adultery with your neighbor's wife." Then Allah, the Mighty and Sublime, revealed the following words confirming that: "And those who invoke not any other Ilah (god) along with Allah, nor kill such person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment.