Quran 24:6 — Light (Al-Noor)

وَالَّذينَ يَرمونَ أَزوٰجَهُم وَلَم يَكُن لَهُم شُهَداءُ إِلّا أَنفُسُهُم فَشَهٰدَةُ أَحَدِهِم أَربَعُ شَهٰدٰتٍ بِاللَّهِ ۙ إِنَّهُ لَمِنَ الصّٰدِقينَ

As for those who accuse their own spouses, without any other witnesses, then the testimony may be accepted if he swears by GOD four times that he is telling the truth.

[24:5] If they repent afterwards and reform, then GOD is Forgiver, Merciful.

[24:7] The fifth oath shall be to incur GOD's condemnation upon him, if he was lying.