Source: Fatāwā Amunpuri by Shaykh Ghulām Mustafa Zaheer Amunpuri
❖ Question:
What is the ruling on marrying the daughter of a foster brother (raḍāʿī brother)?
✿ Answer:
Marriage to the daughter of a foster brother is not permissible.
Such a girl is considered one’s foster niece, and the man is her foster paternal uncle (raḍāʿī chachā). Just as marriage between a biological uncle and his niece is forbidden, so too is marriage between a foster uncle and his foster niece.
❀ Allah ﷻ says:
﴿وَبَنَاتُ الْأَخِ﴾
“And [forbidden to you are] the daughters of your brothers.”
📚 Surah al-Nisā’ (4): 23
This prohibition includes both biological and foster nieces, as the wording of the verse is general and applies to all forms of brotherhood—whether by blood (nasab) or by breastfeeding (raḍāʿah).
✅ Conclusion:
① A man’s foster brother’s daughter is his foster niece.
② Such a relationship falls under the prohibited degrees of marriage.
③ Therefore, nikāḥ with a foster niece is ḥarām (forbidden and invalid) in Islam.
