All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His Slave and Messenger.
For more benefit, please refer to Fatwa 174781.
If it has been proven by means of clear and strong evidence that the wife has committed a disgraceful offense (bringing disgrace to her spouse's honor), her denial should not be taken into account. Instead, it is incumbent on the husband to be firm in forbidding her from such disgraceful conduct. Allaah, The Exalted, made the husband responsible for his wife, her protector and maintainer. Allaah, The Exalted, says (what means): {Men are in charge of women by [right of] what Allaah has given one over the other and what they spend [for maintenance] from their wealth...} [Quran 4:34]
Therefore, the husband should advise his wife and remind her of Allaah, The Exalted. He should alienate her in bed and threaten her of divorce as perhaps she would confess her sin and express regret and remorse for what she had committed. If she does so, then it is good; otherwise, if the husband feared for his marriage and sensed her persistence in carrying on with this sinful relationship, it is better for him to divorce her.
For more benefit, please refer to Fataawa 81356 and 131584.
Allaah knows best.