ما هو الحديث النبوي الذي يحرم على الرجل أن يتزوج امرأة ويشترط أهلها تطليق زوجته الأولى؟ وما حكم الشرع في ذلك؟

It is not permissible for a Muslim to enter into a relationship with a woman who is unlawful to him with the intention of marriage; rather, he should approach her guardians to propose to her. He is permitted to look at her face and hands. It is not lawful for a woman to request the divorce of her sister. However, it is not religiously forbidden for a man to divorce his wife and marry another. Divorce may be preferable in some cases, such as when there is an irreconcilable dispute. If it is possible to keep both wives and be just between them, that is better. Otherwise, he should weigh the benefit of remaining with his wife against the benefit of separating from her and marrying another, remembering the Prophet Muhammad's (peace be upon him) saying: "A believing man should not hate a believing woman; if he dislikes one of her characteristics, he will be pleased with another."