Source: Fatāwā Amunpuri by Shaykh Ghulam Mustafa Zaheer Amunpuri
What is the ruling on marrying a wife’s illegitimate sister while the wife is still in marriage?
It is not permissible to marry the illegitimate sister of one’s wife while the wife is still married.
Such a marriage is forbidden (ḥarām) and invalid in Islamic law.
Allah ﷻ says:
﴿ وَأَنْ تَجْمَعُوا بَيْنَ الْأُخْتَيْنِ ﴾
Sūrat al-Nisā’ (4): 23
“And (also forbidden is) that you combine two sisters (in marriage at the same time).”
This ruling includes all types of sisters, even if the relationship is due to illegitimate birth —
i.e., the woman who was born from the same father, even through an unlawful relationship, is still considered a sister in lineage under Islamic law for the purposes of this ruling.
Thus, the illegitimate sister of the wife is also included in the prohibition mentioned in the verse.
① It is haram to marry one’s wife and her sister — whether legitimate or illegitimate — at the same time.
② The illegitimate sister, born from the same father, is included in the definition of "sister" for this ruling.
③ Such a marriage is void and forbidden in Islam.
❖ Question:
What is the ruling on marrying a wife’s illegitimate sister while the wife is still in marriage?
✿ Answer:
It is not permissible to marry the illegitimate sister of one’s wife while the wife is still married.
Such a marriage is forbidden (ḥarām) and invalid in Islamic law.
Allah ﷻ says:
﴿ وَأَنْ تَجْمَعُوا بَيْنَ الْأُخْتَيْنِ ﴾
Sūrat al-Nisā’ (4): 23“And (also forbidden is) that you combine two sisters (in marriage at the same time).”
This ruling includes all types of sisters, even if the relationship is due to illegitimate birth —
i.e., the woman who was born from the same father, even through an unlawful relationship, is still considered a sister in lineage under Islamic law for the purposes of this ruling.
Thus, the illegitimate sister of the wife is also included in the prohibition mentioned in the verse.
✔ Summary:
① It is haram to marry one’s wife and her sister — whether legitimate or illegitimate — at the same time.
② The illegitimate sister, born from the same father, is included in the definition of "sister" for this ruling.
③ Such a marriage is void and forbidden in Islam.
