Ruling on a man marrying a girl with whom he shared breastfeeding from a woman

Question:
A girl and a boy were breastfed by their aunt. Is it permissible for the boy to marry this girl?

Answer:
If a boy and a girl are breastfed by any woman, they become siblings, whether she is their aunt, their cousin’s mother, or a distant relative. If they are breastfed by any woman, they become siblings if the breastfeeding meets the legal requirements, meaning if it is five feedings or more within the first two years. In that case, they become siblings, even if the woman who breastfed them is a complete stranger to both of them. He is not permitted to marry her, because she has become his sister through breastfeeding, provided the breastfeeding was five feedings or more and occurred within the first two years, not after them. This is what the Shari'ah has established based on the report of the Prophet (peace and blessings be upon him).