Breast-feeding Which Brings About Prohibition

Question :

My father has a wife who is not my mother and she has children from my father. We have an aunt, my mother's sister, who breast-fed me and my brothers born of my mother, and she has children, both male and female. My question is, is it permissible for my brothers from my father to sit and talk with the daughters of my maternal aunt, without them wearing a veil, bearing in mind that my brothers from my father did not complete their breast- feeding from my aunt, who is my mother's sister. Do the sons and daughters of my maternal aunt become brothers to us all?

Answer:

It is not permissible for your brothers who were not breast-fed by your maternal aunt to consider themselves Mahrams for her daughters, because they were not breast-fed by her. The Mahrams of your aunt's daughters are only those who were given a complete breast-feeding by her which is five breast-feedings or more, while they were in the first two years of life. This is based upon the saying of the Prophet ﷺ:
"There is no breast-feeding except in the (first) two years."

And, according to the narration confirmed 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." Narrated by Muslim in his Sahih and by At-Tirmithi in his Jami', and this is his wording.

The Prophet ﷺ also said:
"That which is forbidden due to kinship is forbidden due to breast- feeding."

Source:
Ibn Baz
Fatawa Islamiyah, Vol. 6 Pages 131-132