Q: I have a brother whose wife begot him a daughter. The mother of the daughter used to leave her to our mother whenever she wanted to fetch water, which would take her a long time. Missing her mother, the baby would cry. Our mother found herself forced to offer her her breast so as to stop the baby's crying. Our mother said that she repeated this many times and that
when squeezing her nipple, it would produce milk mixed with water.
Being asked about the amount of milk she gave the baby, my mother told me that it was about a small cup. This was done by my mother when she had last given birth to a child who was 15 years old at the time. Is this girl permitted to marry my son?
If the case is as you have mentioned, that your mother suckled the daughter of your brother many times and that at that time she produced little milk mixed with water, then the daughter of your brother who was suckled by your mother becomes your sister through breastfeeding ties and a paternal aunt to your son if she was suckled from your mother five times or more in her first two years of age. Accordingly, it is not permissible for your son to marry this girl. (Part No. 21; Page No. 54) Allah (Exalted be He) says:
Forbidden to you (for marriage) are: your mothers, your daughters
to His saying:
...your father’s sisters, your mother’s sisters, your brother’s daughters, your sister’s daughters
It was authentically reported that
`Aishah (may Allah be pleased with her) said: "It was revealed in the Qur'an that ten clear breastfeeding prohibit (marriage) then it was abrogated (and substituted) by five clear breastfeedings, and Allah's Messenger (peace be upon him) died while it was likewise." On the other hand, if she had less than five times of breastfeeding or if she was suckled after her first two years of age, it is permissible for your son to marry her. It is worth mentioning that if a baby sucks even a little milk from the breast and then leaves it, this is considered one breastfeeding. If it again sucks even a little milk and then leaves it, this is considered a second breastfeeding, etc.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.