An-Nur 24:6

وَٱلَّذِينَ يَرْمُونَ أَزْوَٰجَهُمْ وَلَمْ يَكُن لَّهُمْ شُهَدَآءُ إِلَّآ أَنفُسُهُمْ فَشَهَٰدَةُ أَحَدِهِمْ أَرْبَعُ شَهَٰدَٰتٍۭ بِٱللَّهِ ۙ إِنَّهُۥ لَمِنَ ٱلصَّٰدِقِينَ

And for those who launch a charge against their spouses, and have (in support) no evidence but their own,- their solitary evidence (can be received) if they bear witness four times (with an oath) by Allah that they are solemnly telling the truth;