Qur'an 24:2

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

The adulterer and the adulteress, scourge ye each one of them (with) a hundred stripes. And let not pity for the twain withhold you from obedience to Allah, if ye believe in Allah and the Last Day. And let a party of believers witness their punishment.