Is it obligatory to perform Istibra' (period of waiting/purification) for a slave woman purchased by her existing husband?
General Chapter
Al-Mughni
Book of Waiting Periods ('Iddah)
Primary text
It is not obligatory to perform Istibra' for a slave woman whom a man purchases if he is already her husband, because she is considered his established property (firash). Therefore, purification from his own semen is not required. However, performing Istibra' is recommended (mustahabb) to ascertain the paternity of any resulting child and to determine the resulting legal status of the woman regarding Wala' (allegiance/custody) and the status of Umm Walad (mother of one's child).
Supporting text
The recommendation stems from uncertainty regarding the child's origin: if the child is conceived through the marital bond, the Wala' belongs to the husband because the liberation occurs through his ownership, and the slave woman does not become an Umm Walad. If the child is conceived subsequent to ownership, the Wala' does not apply, and she becomes an Umm Walad.