Yet some who undertake to issue fatwas may take a strict approach to these matters because they are unclear to those seeking rulings, who do not describe what they are asking about using the names and distinctions relevant under Islamic law. Someone might ask, for example: “Two people have become siblings through breastfeeding. May one marry the other’s sister?” This question lacks sufficient detail. The breastfed person himself may not marry any of the other’s sisters born to the mother who breastfed him. If, however, the other has sisters born to a different mother, they are unrelated to the breastfed person, and he may marry any of them.

Likewise, someone might ask: “A boy and a girl, or two boys, have become siblings through breastfeeding. May either marry a sibling of the other, and may the sisters on either side marry into the other family?” The answer is that the brothers of either breastfeeding sibling may marry the sisters of the other, provided that the prospective husband was not breastfed by the prospective wife’s mother, nor the prospective wife by the prospective husband’s mother. The scholars agree on this.

As for the two breastfeeding siblings themselves, neither may marry any of the wet nurse’s children. Thus, neither may marry a sibling of the other who shares the mother who breastfed him or the father to whom the milk is attributed. Each may, however, marry a sibling of the other who is not a child of either of his own parents through breastfeeding. This answers the various cases in question.

The possibilities are for the breastfed child to marry a sibling of the other breastfed child through that woman or man, or to marry a sibling of the other through blood relationship or through another breastfeeding relationship. The breastfed child’s siblings, in turn, might marry someone from the first, second, or third of these groups.

The breastfed child’s siblings may marry any of them: the wet nurse’s children