We have reviewed request no. 2631 for the year 2005, which includes the following:
Question
A woman breastfed a young woman along with her other children. Now, the grandson of this woman's husband intends to marry this young woman. Note, that the number of nursings exceeded four times. What is the ruling on this marriage?

 

When a woman nurses a child, she becomes its mother, and the husband who caused her milk to flow [by impregnating her], becomes its father. In Islamic terminology this milk is referred to as Laban al-Fahl.
The Ruling
It is forbidden for this man to marry the young woman because she became his aunt-through-nursing. In Islamic law it is forbidden to marry an aunt-through-nursing just as it is forbidden to marry an aunt who is a blood relative.
And Allah, the Majestic, knows best.