Ruling 2501 — Breastfeeding

A man cannot marry two sisters, even if they are nursing sisters, meaning that they are sisters to each other through breastfeeding. In the event that he marries two sisters and later realises that they are sisters, then, if the marriage contracts were concluded at the same time, both marriage contracts are void. However, if they were not concluded at the same time, the marriage contract of the first is valid (ṣaḥīḥ) and the marriage contract of the second is void.