the Prophet—may Allah bless him and grant him peace—who told her, ‘Give him permission to enter, for he is your uncle.’ ‘Ā’ishah said, ‘It was the woman who breastfed me, not the man.’ He replied, ‘He is your uncle, so let him enter your presence.’”

He also said:

“What is forbidden through blood relationship is also forbidden through breastfeeding.”

When the man and woman become the parents of the breastfed child, all their children become that child’s siblings, whether they are children of the father alone, the woman alone, or both, or are their children through breastfeeding. All become siblings of this child through breastfeeding. Thus, even if a man has two wives, one of whom breastfeeds a boy and the other a girl, the two children become siblings and may not marry one another, according to the agreement of the four imams and the majority of Muslim scholars.

Ibn ‘Abbās was asked about this “question” and replied, “The source of conception is one and the same”—meaning that the man whose intercourse with the two women brought about their lactation is one and the same.

By the agreement of the Muslims, there is no distinction between the woman’s children who nursed alongside the child and those born to her before or after the breastfeeding. Muslims are agreed on this.

The belief held by many ignorant people—that marriage is forbidden only to someone who nursed alongside the child—is misguidance for anyone who holds it unless he abandons it. If he persists in considering such a marriage lawful, he is to be called upon to repent, just as anyone else who permits marriage between siblings through breastfeeding is called upon to repent. If he repents, well and good; otherwise, he is to be put to death.

Since this is so, “all the woman’s relatives are relatives of the breastfed child through breastfeeding”: her children are his siblings, her children’s children are his siblings’ children, and her male and female ancestors