Surah An-Nur, verse 2

ٱلزَّانِيَةُ وَٱلزَّانِى فَٱجْلِدُوا۟ كُلَّ وَٰحِدٍ مِّنْهُمَا مِا۟ئَةَ جَلْدَةٍ ۖ وَلَا تَأْخُذْكُم بِهِمَا رَأْفَةٌ فِى دِينِ ٱللَّهِ إِن كُنتُمْ تُؤْمِنُونَ بِٱللَّهِ وَٱلْيَوْمِ ٱلْـَٔاخِرِ ۖ وَلْيَشْهَدْ عَذَابَهُمَا طَآئِفَةٌ مِّنَ ٱلْمُؤْمِنِينَ ﴿٢﴾

24:2 As for the woman and the man who commit fornication; flog each of them a hundred lashes. Do not let pity for them make you lenient concerning the law of Allah, if you believe in Allah and the Last Day. And let a group of the believers witness their punishment