What is the ruling on marriage to the sister of one’s sister through breastfeeding?.
Praise be to Allaah.
If a man has a sister
through breastfeeding, who was breastfed by his mother, or was breastfed
along with him by another woman, he may marry her sister, because the mahram
relationship here is limited only to the one who was breastfed, and not her
But if he was breastfed by
the mother of the girl, then he is a brother to the girl and to all her
sisters, so it is not permissible for him to marry any of them.