The method by which a son fulfills the obligation to provide marriage for his father.
General Chapter
Al-Mughni
Book of Maintenance (Nafaqāt)
Primary text
If the son is obligated to provide marriage for his father, he has the choice: he may marry the father to a free woman, or he may procure a female slave (amma) for him, or he may give the father the means to marry a free woman or purchase a female slave. The father does not have the right to choose the method. However, if the father specifies a particular woman and the son specifies another woman, and the dowries are equal, the father's choice prevails because the marriage is for him and the cost is the same. If the dowries differ, the son is not obligated to provide the higher amount, as he is only obligated to provide the minimum amount necessary to satisfy the need.
Supporting text
The son cannot marry the father to a slave woman, nor procure one for him, because this causes harm to the son by enslaving his offspring and diminishing the father's enjoyment. Even if the father consents to being married to a slave woman, it is not permissible because the harm extends to the child.