Is it permissible for the son of a foster daughter to marry the daughter of her son, knowing that the foster mother does not remember the number of sucklings or whether they were sufficient, and that she breastfed eight years after her menstrual cycle ceased and she had no milk?

The ruling on the marriage of the son of the suckling woman's daughter to the daughter of the suckling woman's son revolves around the presence of milk and the number of sucklings.

If the presence of milk is confirmed and five known sucklings have occurred, the prohibition spreads, and her daughter's son becomes an uncle to her son's daughter through suckling, making marriage between them impermissible.

If the presence of milk is confirmed but there is doubt about the number of sucklings, or if the number of sucklings is confirmed but there is doubt about the original presence of milk, it is safer not to marry, out of consideration for the difference of opinion. The general principle is that prohibition does not apply in cases of doubt, but piety dictates refraining from marriage.

The majority of scholars do not stipulate a prior pregnancy for the establishment of prohibition; they hold that the milk of a virgin woman causes prohibition. However, the Hanbalis, within their madhhab, are of the view that the milk of a virgin woman does not spread prohibition. It is also not a condition for the suckling woman to be of menstruating age.