The first condition is that the child must receive five or more distinct nursings. ʿĀʾishah (may Allah be pleased with her) related: “There was revealed in the Qur’an: ‘Ten well-known sucklings make marriage unlawful.’ Then it was abrogated to ‘five sucklings,’ and it remained ‘five well-known sucklings make marriage unlawful.’ The Messenger of Allah ﷺ passed away while this was still being recited.” Narrated by Muslim. This is a case where the wording was abrogated but the ruling remained in force; it clarifies what the verse and the other ḥadiths on nursing had left general.

The second condition is that the five sucklings occur within the first two lunar years, for Allah the Exalted says: “Mothers shall breast-feed their children for two complete years for whoever wishes to complete the nursing” (Qur’an 2:233). This noble verse shows that only the nursing that takes place within those two years is legally effective. The Prophet ﷺ also said: “Nothing renders unlawful through nursing except what opens the intestines and is before weaning.” Al-Tirmidhī declared this report “good and sound.” In other words, only the nursing that reaches the intestines and fills them establishes the prohibition; a negligible amount that does not reach or expand them does not. Likewise, it is effective only when it occurs before weaning—in the period of infancy—when the milk serves as nourishment, satisfies the child’s hunger, and causes his flesh to grow, for at that stage the milk effectively becomes part of him.

As for what counts as a single suckling: it is when the infant latches onto the breast and then breaks off to breathe, to switch to the other breast, or for some other reason; that interruption marks one suckling. If the child resumes, that is counted as a second suckling, and so on, even if all of this happens in the same sitting. The Lawgiver specified the number of sucklings but did not define what constitutes one suckling, so its determination is referred to customary usage.