it be the milk of a human female, for the Almighty says: “your mothers who nursed you…” (4:23).

The second condition is that the child must suckle five separate times or more. If the nursing occurs only once, twice, three, or even four times, it carries no legal effect. Thus, were a woman to nurse an infant on four different days, each time until the child was satisfied, he would still not become her son through suckling, because five feedings are required. Conversely, if she were to nurse him five times— even without his reaching satiety—she would become his foster-mother and the nursing would render marriage between them unlawful.

The third condition is that the suckling take place within the nursing period, namely before weaning in the first two lunar years. If it occurs outside that time—say a woman nurses a child who is already older—it has no effect. Should a five-year-old child nurse from a woman five or even ten times, he would not become her son through nursing, for it falls outside the legally recognized period.

These, then, are the three conditions. Once the prohibition is confirmed, it applies only to the nursling himself and to his descendants; it does not reach his siblings, fathers, or mothers. Accordingly, the biological brother of the nursling may lawfully marry the foster sister of his brother through nursing, because the ruling affects only the nursling and his direct line—that is, his progeny.

As for his ascendants—fathers and mothers—and his collateral relatives—brothers, uncles, their sons and daughters—nursing has no bearing on them, whether they are older or younger than he. The widespread belief among common folk that the younger siblings of the nursling automatically fall under the foster-kinship ruling is therefore unfounded.