“O Prophet, We have made lawful for you your wives whose dowries you have paid, those whom your right hand possesses from what Allah has granted you, and the daughters of your paternal uncles, paternal aunts, maternal uncles and maternal aunts who emigrated with you.”

These “four categories” are the relatives whom one may marry, so their counterparts through breastfeeding may also be married. Since the breastfed child becomes the son of the woman and her husband, his children become their grandchildren, and the same marriage prohibitions apply to his children as apply to biological children. It is through these three lines that the marriage prohibitions arising from breastfeeding extend.

As for the breastfed child’s biological siblings, father and mother, they are unrelated to his father, mother and siblings through breastfeeding. No tie of kinship, whether through blood or breastfeeding, connects the two groups. A man may have a paternal half-brother and a maternal half-brother with no blood relationship between them. Indeed, his paternal half-brother may marry his maternal half-sister. How much more so when one is a brother through blood and the other a sister through breastfeeding: the one may marry the other, and vice versa.

This dispels a misconception that occurs to some people. The breastfed child’s brother through breastfeeding may marry his biological mother, just as he may marry his biological sister. His biological brother may also marry his sister through breastfeeding. This has no counterpart in blood kinship, for a man’s biological brother cannot marry his biological mother. His sister through breastfeeding is neither a daughter nor a stepdaughter of his biological father; she may therefore marry him.