Question:
What is the ruling on marrying the daughter of a foster sister?
Answer:
It is not permissible to marry the daughter of a foster sister, just as it is not permissible to marry the daughter of a biological sister, because the relationships that are prohibited by blood relations are also prohibited by fosterage.
❀ Sayyida Aisha (may Allah be pleased with her) reports that the Messenger of Allah (peace be upon him) said:
إن الرضاعة تحرم ما تحرم الولادة
“Fosterage also makes those relationships unlawful that are made unlawful by birth (blood relations).”
❀ The command of Allah, the Exalted, is:
﴿وَبَنَاتُ الْأُخْتِ﴾
“And the daughters of sisters (are also made unlawful for you).”
Here, the word “أخت” is general, which includes foster sisters as well, therefore, it is not permissible to marry a foster niece, because the relationship that is prohibited by blood is also prohibited by fosterage.
