He—may Allah have mercy on him—was asked:

“A man married a woman and had several children with her. Recently, someone who had a dispute with the wife came forward and told her husband, ‘This woman to whom you are married drank your mother’s milk.’”

He replied:

If this man is known to be truthful, knows the matter he reports, and states that she was breastfed by the husband’s mother on five occasions within the first two years of life, his statement is to be accepted in this matter. Otherwise, accepting it is not obligatory, even if he witnessed the breastfeeding. And Allah knows best.

He—may Allah have mercy on him—was asked:

“A man, when he was a small child, was breastfed by a woman alongside a daughter of hers. This daughter has younger sisters. Are any of them forbidden to him in marriage?”

He replied:

If he was breastfed by a woman on five occasions within the first two years of life, he becomes her son through breastfeeding. All her children, whether born before or after that breastfeeding, are his siblings. This, too, is a matter of consensus among Muslims.