Ruling on marrying a woman from whom a man nursed from her mother’s milk before her father

Question: What is the ruling on a man who married a woman from whom he nursed from her mother’s milk before her father?

Answer: From Abdulaziz ibn Abdullah ibn Baz to the honorable brother S. A. Q. May Allah guide him to all good, amen.
Peace be upon you, and the mercy of Allah and His blessings. After that:
O beloved, your noble letter dated 19/12/1388 AH has reached us, may Allah guide you, and the information it contained regarding a man who married a woman from whom he nursed from her mother’s milk before her father, and your question about the ruling in that matter, was it known?
The answer is: This marriage is invalid; because the man mentioned is the brother of the woman mentioned; due to the fact that he nursed from her mother, and the prohibition of that is known by the Book and the Sunnah and by the consensus of the Muslims, if her mother had breastfed him five times while he was within the two-year period, and it is obligatory to separate them immediately, if the matter is as we have mentioned, but if there is actually a difficulty, then it is obligatory for them to contact the scholars around them and ask them about what is difficult for them. May Allah guide everyone to what brings Him pleasure and to avoiding His prohibitions, He is the Generous, the Bountiful, and peace be upon you and the mercy of Allah and His blessings.