Quran 24:6

وَٱلَّذِينَ يَرۡمُونَ أَزۡوَٲجَهُمۡ وَلَمۡ يَكُن لَّهُمۡ شُہَدَآءُ إِلَّآ أَنفُسُهُمۡ فَشَهَـٰدَةُ أَحَدِهِمۡ أَرۡبَعُ شَہَـٰدَٲتِۭ بِٱللهِ‌ۙ إِنَّهُ ۥ لَمِنَ ٱلصَّـٰدِقِينَ ٦

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