Chapter on laban al-faḥl (paternal milk)

When a woman nurses an infant during the first two years, the child becomes her son and, through the milk, the son of the man whose seed occasioned that milk. Accordingly, it is unlawful for the child to marry any of the daughters of his nursing mother, or any of the daughters of her husband or master, because that man is deemed his father by virtue of the suckling. Nor may he marry any other female relative of that man, except those whom he would likewise be permitted to marry from among the relatives of his own natural father. It is also forbidden for him to marry any woman from among the daughters whom the husband has by another wife, just as it is forbidden for him to marry the nursing mother’s own daughters, whether they are by that husband or by someone else. A child’s child, no matter how far down the line, takes the same ruling as the child himself.

If the milk was produced from illicit intercourse, no prohibition is established on account of the male. And if a man has two wives or two female slaves and one of them breast-feeds