Marrying one’s daughter to a man while doubting they are brother and sister by breastfeeding

Q: A man has a girl who is engaged to a young man. In her childhood, she used to mix with his siblings and I think this young man's mother breastfed this girl. When (Part No. 21; Page No. 130) she was asked about this, she was first a bit hesitant as she does not remember anything about this breastfeeding. Eventually, she resolutely denied that she breastfed the girl. He asks about the validity of giving this girl in marriage to this young man.

A: The fundamental ruling is that breastfeeding does not take place, and things remain unchanged except if proven otherwise. The questioner does not have, as he mentioned, any proven evidence to change what is certain. Having mixed with his siblings during childhood is not sufficient evidence to prove that breastfeeding occurred. Therefore, if it is not certain that the girl or the young man was breastfed by any of this man's wives for five times, or that both of them were breastfed together by one woman, then their marriage to each other is permissible. It is not affected by her having mixed with his siblings when she was suckling.May Allah grant us success. May peace and blessings be upon our Prophet, his family and Companions.