Q: How many times does another’s child have to breastfeed to be considered a part of the wet-nurse’s family?
A: Nursing is defined as suckling milk, which was produced by pregnancy, within two years of the nursing child's life, from the breast of a woman and drinking it, or consuming it in some other way like eating it after it has curdled, ingesting it through the nose, or drinking it without the breast e.g. from a bottle. It can also be consumed mixed with something else so long as the milk is the dominant ingredient such that its qualities are still obvious. Injecting the milk is not considered nursing.
In Islām, the act of nursing another’s child prohibits what birth prohibits. Essentially the child becomes a part of the wet-nurse’s family as well as the family of the man from whom the milk was produced i.e. the legal partner in the wet-nurse’s pregnancy which resulted in the milk production. Specifically, the child, male or female, is no longer a potential for marriage and is not obliged to adhere to the rules of hijab and seclusion.
The child is considered their child and the child’s offspring their grandchildren. The parents’ children, from them as a couple or from other spouses, become the child’s siblings, their parents become the child’s grandparents, and their siblings become the child’s uncles and aunts. These rules do not apply beyond the nursed child to his/her biological relatives.
This relationship does not oblige financial maintenance, inheritance, manumission, or rejection of testimony, etc.
Two conditions must be met for this to apply.
1. The child must consume her breast milk within the first two hijra years of his/her life and not a moment later.
2. They must nurse at least five times. The moment the child suckles the breast and then releases, even if the release was forced, to catch their breath, due to distraction or boredom, to move from one breast to another, or to move from one wet-nurse to another, it is counted as one nursing. When they return to the breast, even if within a short period of time, it is considered an additional or second nursing. There is no specified amount of milk which must be consumed or time between feedings that must be adhered to. Ingesting the milk in other modes would be treated in a similar fashion.
Allāh knows best.
Source: Sharh al-Muntaha, Kashshaf al-Qina’