according to the authoritative position.
If one of two joint owners concludes a kitābah for only his share of the slave, the contract is invalid whenever the remaining share belongs to someone else who has not authorized it; and, according to the school, it is still invalid even if that co-owner gives permission or if the rest of the slave also belongs to the same master.
However, if both owners execute the kitābah together, or jointly appoint an agent to do so, the contract is valid provided the instalment dates coincide and the price is divided in proportion to their respective shares.
Should the slave default, so that one owner declares him in default while the other wishes to keep the contract alive, the matter is treated as though a new contract were being initiated—although another opinion allows the continuation.
If a co-owner waives his portion of the price or frees his share outright, that share is emancipated, and the remainder is appraised if he is solvent.

Section
The master is obliged either to remit part of the price or to advance it to the slave; remission is preferable, and it is most appropriate that this be done with the final instalment. The sounder opinion is that any amount that can properly be called “a portion” fulfils the obligation; its size is not tied to the total price, and its due date may be set before emancipation. It is recommended that he remit a quarter; if not, then at least a seventh.

Intercourse with a female mukatab is forbidden. No hadd penalty is incurred, but a dowry becomes due; the child is born free, and—according to the preferred view—the master is not liable for its monetary value. She thereby becomes a mukatab who has borne her master a child. If she later defaults and the master dies, she is freed. Her children, whether conceived in lawful marriage or through fornication, are—according to the authoritative view—also mukatab; they follow her in both slavery and emancipation, and nothing is owed on their account. The right in this matter belongs to the master, though another opinion assigns it to her. If such a child is killed, its value goes to whoever holds that right. The prevailing position is that compensation for any injury to the child, along with his earnings and bridewealth, is expended on him; whatever remains is held in trust. If he is later emancipated it belongs to him; otherwise, it reverts to the master.

No part of a mukatab is emancipated until the entire price has been paid. If the slave produces payment and the master protests, “This money is unlawful,” yet has no proof, the mukatab swears that it is lawful; the master is then told either to accept it or to remit the debt. If he refuses, the judge takes the payment. Should the mukatab decline the oath, the master swears instead.

If the money delivered is later found to have been usurped, the master must return its equivalent. If this happens with the final instalment, emancipation is deemed not to have taken effect—unless, at the moment of receiving it, the master had already declared, “You are free.” If the money itself proves defective, the master may return it and receive a sound replacement.

The mukatab may not marry without his master’s permission, and—according to the authoritative view—he may not take a concubine even with that permission.