The specification (naming) is invalid, and the dowry of the like (mahr al-mithl) becomes obligatory. This is the opinion of al-Shafi'i; because neither of the two [women] was satisfied with the specified [amount] except on the condition that her guardian marry [the other man] to her companion, thereby decreasing the dowry due to this condition, and [this condition] is void. Thus, when we need to guarantee the reduction, the specified [amount] becomes unknown, so it is void. The second view, which the Qadi mentioned in "al-Jami'", is that the specified [amount] is obligatory; because he mentioned a known quantity that is suitable to be a dowry, so it is valid, just as if he said: "I marry you my daughter for one thousand, on the condition that I have one hundred of it." And Allah knows best.

Section: If he specifies a dowry for one of them but not for the other, Abu Bakr said: The marriage is invalid in both cases; because it became invalid in one of them, so it became invalid in the other. The preferred view is that it is invalid in the one for whom he did not specify a dowry; because her marriage was devoid of a dowry separate from the marriage of the other. And regarding the one for whom he did specify a dowry, there are two narrations; because it contains both a specification and a condition, so it resembles the case where he specified a dowry for each of them. The Qadi mentioned it in this manner.

Section: If he says: "I marry you this slave-girl of mine, on the condition that you marry me your daughter, and her physical person (raqaba) shall be a dowry for your daughter," the marriage of the slave-girl is not valid, according to the analogy of the school; because he did not assign her a dowry other than the marriage of his daughter. And if he marries his daughter to him on the condition that he makes the physical person of the slave-girl a dowry for her, it is valid; because the slave-girl is suitable to be a dowry. And if one marries his slave to a woman, and makes [the slave's] physical person a dowry for her, the dowry is not valid; because the woman's ownership of her husband prevents the validity of the marriage, so the dowry becomes invalid, the marriage is valid, and the dowry of the like becomes obligatory.