What is the scope of the prohibition spread to the nursed child's relatives?
General Chapter
Al-Mughni
Book of Fosterage (Breastfeeding)
Primary text
The prohibition spreads to the nursed child and his descendants, descending in rank, but it does not spread to those in his rank, such as his siblings, nor to those above him, like his father, mother, paternal uncles, aunts, maternal uncles, aunts, grandfathers, and grandmothers. Therefore, the father of the nursed child, his brother, his uncle, or his maternal uncle are not prohibited to the wet nurse for marriage. Likewise, the husband of the wet nurse is not prohibited from marrying the mother of the nursed child, his sister, paternal aunt, or maternal aunt. It is permissible for the children of the wet nurse and the children of her husband to marry the brothers and sisters of the nursed child.
Supporting text
Ahmad stated that it is permissible for a man to marry the sister of his nursing sister when there is no nursing relationship or lineage between them, but only between the female child and her sister (i.e., the sisters share the same nursing mother). Regarding the nursed child, the prohibition spreads to him and his children, but not to those on the same level (siblings) or above him (parents, uncles, aunts, grandparents).