“If either spouse, that spouse’s free child, or that spouse’s mukātab purchases the other spouse, or a share of him or her, their marriage is annulled.” …
His statement, “If either spouse, that spouse’s free child, or that spouse’s mukātab purchases the other spouse, or a share of him or her, their marriage is annulled”: this issue is based on what has preceded. For example, a free woman is married to a slave owned by a man, and she purchases him; the marriage is then annulled, because by purchasing him she becomes his mistress, and a mistress may not marry her slave. If marriage is precluded from the outset, it is likewise precluded from continuing.
Conversely, suppose a free man who is permitted to marry female slaves wishes to marry a slave woman. He marries her, then purchases her. The marriage is annulled, because once he has purchased her, he owns her. Thus, the higher contract supersedes the lower contract, causing the latter to be annulled, and she becomes lawful to him by virtue of his ownership.
Must he observe a waiting period to establish that she is not pregnant, or not? This requires further detail. If her master stipulated ownership of what was in her womb, then he may not have intercourse with her until her womb has been cleared, because the child belongs to the master. But if the master did not stipulate this, then he may have intercourse with her and need not establish that her womb is clear, because the child belongs to him.
His statement, “or that spouse’s child,” is based on the view that a man may not marry his son’s slave woman. The more correct view is that this is permissible. An example is a man who validly marries a slave woman, subject to the well-known conditions. Then his son purchases this wife from her master, and she becomes the son’s property. According to this view, the marriage is annulled, because the father may not marry his son’s slave woman.
It has previously been mentioned that the more correct view is that a father may marry his son’s slave woman unless he comes to own her, and that the marriage is not annulled.