Is one considered a mahram (non-marriageable relative) to the women his non-Muslim father is in a relationship with?
2-9-2024 | IslamWeb
Question:
Assalamualaikum wa rahmatulahi wa barakatuh.My father is a non-Muslim. He was married to my mother but does not want to marry again.My question: Am I a mahram to the women my father is in a relationship with, since we cannot marry our father's wives as mentioned in the Quran?
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
The ruling on the son’s marriage to a woman with whom his father committed adultery (we seek refuge in Allah) is a controversial matter among scholars, and forbidding this marriage is safer. Ibn Qudamah
stated in Al-Mughni: “Unlawful sexual intercourse with a woman makes her unlawful to marry for certain male relatives of the man who committed it, as in the case of the lawful intercourse or the intercourse that took place in a doubtful marriage. This applies to Hurmat-ul-Musaharah (which means that a person becomes permanently forbidden to marry certain relatives of the partner due to the relationship of the marriage). Therefore, if a man commits Zina (fornication/adultery) with a woman, she becomes unmarriageable to his father and his son, and her mother and daughter become unmarriageable to him. A similar opinion was narrated on the authority of `Imran ibn Husayn and was adopted by Al-Hasan, `Ataa’, Tawus, Mujahid, Ash-Sha`abi, An-Nakha`i, Ath-Thawri, Is-haq, and As-hab-ur-Ra'y (scholars, especially the Hanafis, who exercised personal reasoning to reach judgments in the absence of clear texts). On the other hand, Ibn `Abbas 
narrated that unlawful sexual intercourse with a woman does not make her unlawful to marry for certain male relatives of the man who committed it, and this opinion was held by Sa`id ibn Al-Musayyib, Yahya ibn Ya`mur, `Urwah, Az-Zuhri, Malik, Ash-Shafi`i, Abu Thawr, and Ibn Al-Mundhir.” [End quote]
You should also know the fact that the woman with whom the father committed Zina is unmarriageable to the son does not mean she has become a Mahram (a woman who is permanently unmarriageable for him because of a permissible reason, like mother, daughter, sister, etc), but she is still non-Mahram (a woman who has to wear Hijab in front of him). Ibn Qudamah stated in Al-Mughni: “There are three types of intercourse: ……….Third: The absolute forbidden type (Zina) is confirmed to create unmarriageable relation, according to the aforementioned disagreement, but it does not make people involved in it Mahram to each other and does not make it lawful for them to look at each other (as in the case of Mahram relatives).” [End quote]
We note that the Muslim is not allowed to marry a non-Muslim woman except a chaste woman from the People of the Book. It was stated in Al-Eeji’s Tafsir: “Most of the Salaf (the righteous predecessors) held the opinion that it is not permissible to marry the Dhimmiyyah (a non-Muslim woman living under the Islamic rule) who committed Zina (before repentance).” [End quote]
It is also impermissible to marry an unchaste Muslim woman. Ibn Qudamah stated in Al-Mughni: “If a woman committed Zina, it is unlawful for the person who knows this to marry her except under two conditions: First: The elapse of her `Iddah (waiting period after Zina). Second: She should repent to Allah from ZIna.” [End quote]
We note also that it is unlawful for a Muslim woman to marry a disbeliever because this relationship is not considered marriage, but it is considered Zina.
Allah knows best.