Surah An-Nur, Verse 6

وَٱلَّذِينَ يَرۡمُونَ أَزۡوَٰجَهُمۡ وَلَمۡ يَكُن لَّهُمۡ شُهَدَآءُ إِلَّآ أَنفُسُهُمۡ فَشَهَٰدَةُ أَحَدِهِمۡ أَرۡبَعُ شَهَٰدَٰتِۭ بِٱللَّهِ إِنَّهُۥ لَمِنَ ٱلصَّٰدِقِينَ٦

wa-alladhīna yarmūna azwājahum walam yakun lahum shuhadāu illā anfusuhum fashahādatu aḥadihim arbaʿu shahādātin bil-lahi innahu lamina l-ṣādiqīna

And those who accuse their wives [of adultery] and have no witnesses except themselves - then the witness of one of them [shall be] four testimonies [swearing] by Allāh that indeed, he is of the truthful.