Is it permissible for a woman to give her husband a magic potion (sihr) to prevent him from marrying another, and is she sinful if she does so with the intention of preserving her family and her husband?

The husband is obligated to fulfill the condition set by his wife that he will not marry another. It does not matter if this condition was not written in the contract, provided it was stipulated before or during the marriage. The wife must repent to Allah for having bewitched her husband, as this is one of the seven destructive sins. She must seek his forgiveness, unless doing so would lead to a greater harm. Alternatively, she can seek his forgiveness generally, without specifying the nature of the wrong. She must also strive to remove the magic from him using the Qur'an and prophetic supplications.