Thus, whatever Allah has commanded to be maintained is an obligation He has imposed. Whatever a person has pledged to do is an obligation he has undertaken himself; he must therefore fulfill the covenant of Allah and not break his pledge, provided that it does not contradict the Book of Allah.
A person may stipulate a condition contrary to the Book of Allah, intending thereby to make lawful what Allah has forbidden. For example, he may sell or emancipate a slave woman while stipulating that he may continue to have intercourse with her after she leaves his ownership. Or another person may sell a slave and stipulate that the right of patronage shall belong to him rather than to the emancipator. Or he may marry off his slave woman or female relative and stipulate that any child be attributed to someone other than the father, or to himself. Yet Allah has commanded that a child be attributed to his father, and patronage is a bond like the bond of lineage. Whoever is attributed to someone other than his father, or affiliates himself with patrons other than his own, incurs the curse of Allah, the angels, and all mankind.
An authentic report from the Prophet, may Allah bless him and grant him peace, states:
“He prohibited selling or giving away the right of patronage.”
For this reason, according to the majority of scholars, patronage itself is not inherited; rather, like lineage, it provides a basis for inheritance. The right of patronage belongs to the emancipator’s nearest agnatic relatives. It is thus clear that the hadith is true as transmitted. And Allah knows best.
It is established in the two Sahīh collections that the Prophet, may Allah bless him and grant him peace, said:
“The conditions most deserving of fulfillment are those by which you have made marital intimacy lawful.”
This shows that fulfilling conditions in marriage is even more deserving of priority than fulfilling them in sales. Hence, many earlier and later scholars have said that if a person stipulates a condition contrary to the Book of Allah—for example, that he marry a woman without a dowry, or with an unlawful dowry—the marriage is invalid, as in marriages by exchange without dowries and other such cases. This is the position of Mālik and of Ahmad according to one of the two reports from him.