Permanently unmarriageable female relatives

Q9: A woman left her young child in a small village; thereafter, someone took him and raised him as their own son. Later on, when the boy grew up, he unknowingly married his sister. She gave birth to a boy and then the husband discovered that she was his full sister. What is the ruling on this? What is the ruling on the newborn child? Is he considered to be legally born or a son of Zina (fornication and/or adultery)?

Answer: If the case is as you mentioned, that they did not know of the truth of their kinship at the time of marriage, they are excused, but they must be separated from each other. The boy will be attributed to both of them for being born in legal wedlock. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.

Fatwa no. 6471