Surah An-Nur 24:6

وَٱلَّذِينَ يَرْمُونَ أَزْوَٰجَهُمْ وَلَمْ يَكُن لَّهُمْ شُهَدَآءُ إِلَّآ أَنفُسُهُمْ فَشَهَـٰدَةُ أَحَدِهِمْ أَرْبَعُ شَهَـٰدَٰتٍۭ بِٱللَّهِ ۙ إِنَّهُۥ لَمِنَ ٱلصَّـٰدِقِينَ

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.

Translation: Saheeh International

Tafsir

And those who accuse their wives of fornication but have no witnesses to substantiate this except themselves — which happened with some Companions — then the testimony of one of them fa-shahādatu ahadihim the subject shall be to testify swearing by God four times araba‘a shahādātin is in the accusative as a verbal …

Excerpt from Tafsir al-Jalalayn, commentary on 24:6, via Quran.com. The reader has the full commentary and 9 more tafsirs.