Marriage Based Upon a Mutual Condition is Ash-Shighar

Question :

A man married a woman on the understanding that the bride's brother would marry his sister, and they are both now married and have children, and it is said that they paid different sums as a dowry. Likewise, they married at different times. So what should they do? Should they renew the contract, or is this marriage Ash-Shighar, or what should they do?

Answer:

If they married based upon a mutual condition, then it is Ash-Shighar. Like when a man requests from another that he marry him (to his daughter or sister) in exchange for marrying him to his sister. This is Ash-Shighar which was forbidden by the Prophet So they must renew their wedding contract, without the necessity for divorce, if both of them want their wives and the wives want them. They must renew the contract without the condition of one woman for another, and the man must ask the woman's guardian or her nearest relative among her paternal relations. He must marry him (to her) with a new dowry, and a new contract, and in the presence of two just witness. This is the way. And the other woman likewise, even if it be for a small dowry and even if it be in the house, without going to the Court.

Source:
Ibn Baz
Fatawa Islamiyah, Vol. 5 Page 417