Mishkat al-Masabih, hadith 80

عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّ اللَّهَ كَتَبَ عَلَى ابْنِ آدَمَ حَظَّهُ مِنَ الزِّنَا أَدْرَكَ ذَلِكَ لَا مَحَالَةَ فَزِنَا الْعَيْنِ النَّظَرُ وَزِنَا اللِّسَانِ الْمَنْطِقُ وَالنَّفْسُ تَمَنَّى وَتَشْتَهِي وَالْفَرْجُ يصدق ذَلِك كُله ويكذبه» وَفِي رِوَايَةٍ لِمُسْلِمٍ قَالَ: «كُتِبَ عَلَى ابْنِ آدَمَ نَصِيبُهُ مِنَ الزِّنَا مُدْرِكٌ ذَلِكَ لَا محَالة فالعينان زِنَاهُمَا النَّظَرُ وَالْأُذُنَانِ زِنَاهُمَا الِاسْتِمَاعُ وَاللِّسَانُ زِنَاهُ الْكَلَامُ وَالْيَدُ زِنَاهَا الْبَطْشُ وَالرِّجْلُ زِنَاهَا الْخُطَا وَالْقَلْبُ يَهْوَى وَيَتَمَنَّى وَيُصَدِّقُ ذَلِكَ الْفَرْجُ وَيُكَذِّبُهُ»

Abu Huraira reported God's messenger as saying, “God has decreed for man his portion of fornication which he will inevitably commit. The fornication of the eye consists in looking, and of the tongue in speech. The soul wishes and desires, and the private parts accord with that or reject it.” (Bukhari and Muslim.) In a version by Muslim he said, “Man’s share of fornication which he will inevitably commit is decreed for him. The fornication of the eyes consists in looking, of the ears in hearing, of the tongue in speech, of the hand in violence, and of the foot in walking. The heart lusts and wishes, and the private parts accord with that or reject it.”