Hadithcore
Sahih Muslim, 2763 b
sahih

Ibn Mas'ud reported that a person came to Allah's Messenger (ﷺ) and told him that he had kissed a woman or touched her with his hand or did something like this. He inquired of him about its expiation. It was (on this occasion) that Allah, the Exalted and Glorious, revealed this verse (as mentioned above).

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، حَدَّثَنَا الْمُعْتَمِرُ، عَنْ أَبِيهِ، حَدَّثَنَا أَبُو عُثْمَانَ، عَنِ ابْنِ، مَسْعُودٍ أَنَّ رَجُلاً، أَتَى النَّبِيَّ صلى الله عليه وسلم فَذَكَرَ أَنَّهُ أَصَابَ مِنِ امْرَأَةٍ إِمَّا قُبْلَةً أَوْ مَسًّا بِيَدٍ أَوْ شَيْئًا كَأَنَّهُ يَسْأَلُ عَنْ كَفَّارَتِهَا - قَالَ - فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ ‏.‏ ثُمَّ ذَكَرَ بِمِثْلِ حَدِيثِ يَزِيدَ ‏.‏

References2 variants
In-Book Reference
Book 50, Hadith 48
USC-MSA web (English) reference
Book 37, Hadith 6656 (deprecated numbering scheme)