What is the status of the offspring resulting from the father's intercourse with his son's slave?
Chapter on What is Prohibited to Marry and Combining Between Them and Other Matters
Al-Mughni
Book of Marriage
Primary text
If the slave becomes pregnant from the father, the resulting child is free (Hurr) and lineage is established with the father because the act involved intercourse where Hadd was waived due to doubt. This status is analogous to the offspring of a jointly owned female slave (Mullakat Ishtirak). Consequently, the female slave becomes an Umm Walad (mother of a free child) to the father.
Supporting text
Shafi'i, in one of his two opinions, stated that she does not become an Umm Walad because she was not lawfully owned by the father, similar to when a man has intercourse with a stranger's female slave under a misconception (shubha).