Is it permissible to marry a female slave who has not completed her waiting period (istibra') to someone other than her current owner?
General Chapter
Al-Mughni
Book of Waiting Periods ('Iddah)
Primary text
If the purchaser has not freed the slave, he is prohibited from marrying her to another man before her istibra' is completed, because she is one for whom istibra' is obligatory, making marriage impermissible, similar to a woman observing the waiting period ('idda). This prohibition applies whether she was bought from someone who had sexual relations with her, someone who completed her istibra' but did not have intercourse, or someone incapable of intercourse, such as a minor, a woman, or one who was castrated. The evidence for this is the general ruling of the Prophet, peace and blessings be upon him: "A woman who has not conceived shall not be approached until she is proven chaste by one menstrual cycle." Furthermore, since it is forbidden for the purchaser to have sexual intercourse with her before istibra', it is also forbidden for him to facilitate her marriage, just as if her previous owner had sexual relations with her.
Supporting text
Al-Shafi'i permits the purchaser to marry her to another man if he frees her first, even if she had not completed her istibra'. This is because, upon being freed, she becomes a free woman who was not previously subject to sexual access by her owner ('frash'), thus permitting her marriage. This is contrasted with a slave woman who was sexually possessed by her owner, as upon manumission, she must complete her waiting period, which prevents marriage, just like a woman observing 'idda'. Furthermore, if the original owner sought to marry her, he was prevented from doing so because he was not permitted to have intercourse with her via ownership rights ('milk al-yamin'), thus marriage was disallowed for him, unlike the purchaser who might use this as a pretext to bypass the necessity of istibra'.