An-Nur 24:6

Wallatheena yarmoona azwajahumwalam yakun lahum shuhadao illa anfusuhum fashahadatuahadihim arbaAAu shahadatin billahiinnahu lamina assadiqeen

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.

Those who accuse their wives (of adultery) while they have no witnesses except their own selves, then the evidence of one of them would be to swear four oaths by Allah that he is truthful,