The ruling on a man marrying a woman who was breastfed with his sister

Question:
I have a cousin (maternal) whom I want to marry, but her family refused on the grounds that she is my sister through breastfeeding, while my family told me otherwise. The breastfeeding occurred between my cousin and my sister. Does this prevent me from marrying my cousin or not? Please advise us; may Allah reward you.

Answer:
In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, and may Allah send blessings and peace upon the Messenger of Allah, his family, and his Companions, and upon those who follow his guidance. As for what follows, complete breastfeeding that meets its conditions prevents marriage. So this matter you mentioned should be brought before the court so that they can look into the issue. The wet nurse should be present and asked about the nature of the breastfeeding, and the court will see what is sufficient, if Allah wills. Do not proceed with the marriage except with clarity and knowledge that there is safety for your religion from what Allah the Exalted has forbidden for you. Yes. May Allah bless you.