Is His Sister Through Breast-feeding a Sister to All of His Brothers?

Question :

A person is the third among his brothers, and he was breast-fed along with a girl from another family. Is this girl considered to be a sister to all of his brothers, whether younger or older than he, or not? And likewise, (are) his brothers from another mother (also considered her broth- ers)?

Answer:

The breast-feeding which results in prohibition is that which takes place five times or more and which occurs during the first two years of the child's life, according to the Words of Allah, Most High:
"The mothers should suckle their children for two whole years, (that is) for those (parents) who desire to complete the term of suckling."

And, according to the confirmed narration from 'A'ishah, may Allah be pleased with her, in which she said: "It was revealed in the Qur'an that ten known breast-feedings caused prohibition, then it was abrogated by five known breast-feedings. Then the Prophet ﷺ died and the matter remained thus."

One breast-feeding is when the child sucks milk from the breast, then leaves it, either to take a breath, or to transfer to the other breast, or some such thing. Then if he returns, it is a second breast-feeding, and so on. If it is confirmed that the person was breast-fed by the girl's mother, or from the milk of her father's wife, as previously described, then he will be a brother to this girl and to all of her brothers and sisters. Whether they are from the mother and father, or from (only) the father or (only) the mother. As for his brothers, it is permissible for any one of them to marry this girl, or any one of her sisters and there is no effect from this breast-feeding upon the aforementioned marriage.

Source:
The Permanent Committee
Fatawa Islamiyah, Vol. 6 Pages 124-125