Sahih al-Bukhari 6612

مَا رَأَيْتُ شَيْئًا أَشْبَهَ بِاللَّمَمِ مِمَّا قَالَ أَبُو هُرَيْرَةَ عَنِ النَّبِيِّ صلى الله عليه وسلم ‏ "‏ إِنَّ اللَّهَ كَتَبَ عَلَى ابْنِ آدَمَ حَظَّهُ مِنَ الزِّنَا، أَدْرَكَ ذَلِكَ لاَ مَحَالَةَ، فَزِنَا الْعَيْنِ النَّظَرُ، وَزِنَا اللِّسَانِ الْمَنْطِقُ، وَالنَّفْسُ تَمَنَّى وَتَشْتَهِي، وَالْفَرْجُ يُصَدِّقُ ذَلِكَ، وَيُكَذِّبُهُ ‏"‏‏.

“I did not see anything so resembling minor sins as what Abu Huraira said from the Prophet, who said, "Allah has written for the son of Adam his inevitable share of adultery whether he is aware of it or not: The adultery of the eye is the looking (at something which is sinful to look at), and the adultery of the tongue is to utter (what it is unlawful to utter), and the innerself wishes and longs for (adultery) and the private parts turn that into reality or refrain from submitting to the temptation”