﴿ إِلَّا ٱلَّذِينَ تَابُوا۟ مِنۢ بَعْدِ ذَٰلِكَ وَأَصْلَحُوا۟ فَإِنَّ ٱللَّهَ غَفُورٌۭ رَّحِيمٌۭ ﴾

“excepting [from this interdict] only those who afterwards repent and made amends: for, behold, God is much forgiving, a dispenser of grace.”

except those who repent thereafter and make amends in their deeds for God is indeed Forgiving of their unsubstantiated accusations Merciful to them in inspiring them to make repentance whereby their immorality is curbed and their testimony becomes once again acceptable — some say however that it can never be accepted thereafter if the proviso is taken to refer to the last clause.