Narrated Ikrimah:

A man made his wife like the back of his mother. He then had intercourse with her before he atoned for it. He came to the Prophet (ﷺ) and informed him of this matter. He asked (him): What moved you to the action you have committed? He replied: I saw the whiteness of her shins in moon light. He said: Keep away from her until you expiate for your deed.

حَدَّثَنَا إِسْحَاقُ بْنُ إِسْمَاعِيلَ الطَّالْقَانِيُّ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا الْحَكَمُ بْنُ أَبَانَ، عَنْ عِكْرِمَةَ، أَنَّ رَجُلاً، ظَاهَرَ مِنَ امْرَأَتِهِ ثُمَّ وَاقَعَهَا قَبْلَ أَنْ يُكَفِّرَ فَأَتَى النَّبِيَّ صلى الله عليه وسلم فَأَخْبَرَهُ فَقَالَ ‏"‏ مَا حَمَلَكَ عَلَى مَا صَنَعْتَ ‏"‏ ‏.‏ قَالَ رَأَيْتُ بَيَاضَ سَاقَيْهَا فِي الْقَمَرِ ‏.‏ قَالَ ‏"‏ فَاعْتَزِلْهَا حَتَّى تُكَفِّرَ عَنْكَ ‏"‏ ‏.‏