As for “exchange marriage,” they offer several explanations for its invalidity: is it because it entails shared claims to sexual access, because one marriage is made conditional upon the other, or because one contract constitutes an advance against the other? These and other explanations appear in their writings elsewhere.

As for “marriage involving an invalid dower” and “a stipulation excluding the dower,” they uphold the marriage, agreeing with Abū Hanīfah. Their reasoning is that, since marriage is valid without specifying a dower, it is also valid when the dower is expressly excluded. These scholars take temporary marriage as the basis for the marriages they invalidate, and marriage without a specified dower as the basis for those they uphold, while treating exchange marriage as a separate category.

This is the foundation of Abū Hanīfah’s position concerning invalid stipulations in marriage and his distinction between them and invalid stipulations in sales and leases. He held that a sale or lease is not valid without specifying the consideration; hence it is not valid when the consideration is unknown, nor when it contains invalid stipulations. Such stipulations entail uncertainty about the consideration, since the invalid stipulation must be cancelled along with the portion of the price corresponding to it, leaving the remainder of the price unknown.

The majority have argued against these scholars on the basis of the established reports from the Prophet, may Allah bless him and grant him peace, prohibiting exchange marriage and tahlīl marriage, just as he prohibited temporary marriage. A prohibition of a marriage entails its invalidity, as with his prohibition of marriage during the waiting period and marriage without a guardian or witnesses.

They also cite the fact that the Companions invalidated these contracts: they separated spouses in exchange marriages, regarded tahlīl marriage as fornication, threatened the man undertaking it with stoning, and prohibited marriages not entered into out of a genuine desire for married life. We have cited numerous reports from them to this effect in “The Book on the Invalidation of Tahlīl Marriage.” Thus, the invalidity of these marriages is established by the textual evidence and the consensus of the Companions.