Source: Fatāwā Amunpuri by Shaykh Ghulām Muṣṭafā Ẓahīr Amn Pūrī
✿ Question:
If a boy and girl get married and later discover they are foster (milk) siblings, what is the ruling?
✿ Answer:
Once it is confirmed that a prohibited relationship through Riḍāʿah (breastfeeding) exists between the two, immediate separation must take place. The marriage becomes invalid (فسخ).
❀ Evidence:
ʿUqbah bin Ḥārith رضي الله عنه narrated:
“I married the daughter of Abū Ayyāb (Umm Yaḥyā). A dark-skinned woman came and said, ‘I breastfed both of you (i.e., you and your wife).’
I went to the Prophet ﷺ to ask him about it. He turned his face away from me. I asked again, and he turned away again. On the third or fourth time, he ﷺ said:
‘How can she remain with you when it has been said that she breastfed both of you?’
Thus, the Prophet ﷺ prohibited me from remaining with my wife.”
📚 Ṣaḥīḥ al-Bukhārī: 2659
✔ Summary:
✦ If it is proven after marriage that the husband and wife were foster siblings (i.e., both nursed by the same woman),
✦ Their nikāḥ becomes invalid due to the prohibition of marriage between maḥram (non-marriageable) relations established through Riḍāʿah.
✦ Immediate separation is mandatory, as clearly commanded by the Prophet ﷺ.
