Is it permissible for a woman who is being harassed by her daughter's husband to cast a spell on him so that he leaves her alone, in order to protect her household and her daughter's household, after having tried all means to reform him?

Adultery is a grave sin, and it becomes even more heinous and severe when committed with a mahram, such as the wife's mother. Jurists have stipulated that if there is a fear of fitna (temptation or discord) with a mahram, she should be treated like a non-mahram woman to prevent fitna. Therefore, he is not permitted to be alone with her, nor to shake her hand, nor to speak with her except in a permissible manner, and she must observe hijab in front of him.

If she advises him and he does not desist, she should threaten him with informing someone he fears, or by taking his matter to a judge. If she can secure her daughter's release from him, that would be preferable so he distances himself from her.

It is not permissible to perform magic for this purpose.

The afflicted woman is advised not to remain silent about her son-in-law's crime, but rather to deal with his matter wisely, so that it does not affect her reputation or destroy her home.