Man wants to divorce his wife so that his friend can marry her
Is it permissible for a person who has two wives to divorce one of his wives so that his close friend who is unmarried and whom he truly loves for the sake of Allah, can marry her? This is what one of the Companions did. The person who wishes to follow in this Companion's footsteps wants to do this purely for the sake of Allah and for no other reason. He wants to follow the guidance of the Prophet (peace be upon him) that "None of you truly believes until he loves for his brother what he loves for himself” and he wants to be one of those who will be shaded under the throne of Allah on the Day of Judgment.
by the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
It is permissible for a man to divorce his wife if that is what he wants to do.
However, this is not a recommended act. We do not know of all the details of what occurred between the Companions on that one isolated occasion when this took place. We just know that in one isolated instance, a man from the Ansâr in Madinah gave his brother in Islam from the emigrants the choice of one of his wives. We do not even know what the brother had discussed with his wives beforehand. We do not even know if it was his idea or the idea of one of his wives. These were very special circumstances. This was a time when the Muslims were in desperation and weakness and were fleeing from their homeland. The Prophet (peace be upon him) established bonds of brotherhood between the Muslims of Madinah and the Muslims fleeing from Mecca. This was a bond established by none other than the Prophet himself (peace be upon him). This story shows us just how serious the Muslims were about that special and quite unique bond. We should also bear in mind that the other brother declined the offer.
We should realize that a man’s wife has a say in the matter. If she loves her husband, he will be hurting her greatly to even suggest such a thing to her. If he divorces her against her wishes and for no fault on her part, he is not showing her the respect that she deserves. Though Islam permits a man to divorce his wife, it does not encourage it. It recommends that a husband and wife do whatever they can to preserve the marriage bond, even when they are having problems with each other. In cases of difficulty, they should go for arbitration to try and attempt reconciliation before getting a divorce.
Keep in mind that even if he divorces her, she does not have to marry the other man. She does not have to marry anyone she does not wish to marry. If her husband divorces her against her wishes in order to give her to someone else, she will be understandably resentful and it is highly unlikely that she would be willing to marry the other man.
If a man who has two wives truly loves for his brother what he loves for himself, he will help his brother find a wife, pay his dowry on his behalf, and help him get on his feet if he is poor. This is the best way he can help him.
And Allah knows best.