May Allāh give you a good reward. The one who is asking is Um ʿAbd Allāh from Al Madīnah Al‑Nabawiyyah. She is saying in her first question: “I’m a young woman who’s been married for ten years, [still] without child.” She says that her husband—all praise is due to Allāh—treats her well, but he wants to marry again, and “I don’t agree with that.” The question: “Am I sinning by stopping him from getting married again? And would I be sinning if I asked to be separated from my husband if he were to get married to another? Please direct me according to [circumstances] of my question.
Answer from Shaikh Ibn ʿUthaimīn (May Allāh Have Mercy on Him):
The husband has the right to marry of women as he wishes, as Allāh the All-High says [the English meaning of which is]: “And marry whom you please of women: two, three, or four.” [Al-Nisāʾ, 3]. So he has the right to marry up to four, and it is not a right, and it not permissible, for a woman to stop him from marrying another because the right to adding more [wives] belongs to the husband, not the wife, unless she had made it a condition upon him at the time the marital contract [was agreed to] that he not take another wife along with her, since the Messenger ﷺ said: “The most deserving of conditions to fulfill are those by which the private areas [of a woman’s body] become permissible to you.” As for [stopping him] without [having made] a condition, it is not permissible for her to stop her husband, and it is not binding on him to hold himself back from marrying [another] if she were to ask him not to marry. Rather, it is his right to marry [again] whether she likes it or not.
And if he were to marry [another], it is not within her rights to ask him to divorce the other, nor is it permissible for her to request he divorce the other either. And it not binding upon him to divorce her if she were to request that since it has come from the Prophet ﷺ that one who asks her husband for a divorce without a cause of harm will be forbidden the smell of Paradise.