I married two wives. My first wife breast-fed one of the boys of our relatives. Is this boy, whom my first wife had breast-fed, considered as a Mahram (spouse or permanently unmarriageable relative) to my second wife or not?
If the child was breast-fed five times or more from the milk of the first wife during the first two years of his life, the woman's husband becomes the foster-father of the boy. Therefore, the boy becomes a Mahram to the second wife because he is the foster-son of her husband. Allah (Exalted be He) says:
...and not to reveal their adornment except to their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons
It is authentically reported that the Prophet (peace be upon him) said:
Wet-nursing makes unlawful what consanguinity makes unlawful.
It is also authentically reported on the authority of
`Aishah (may Allah be pleased with her) (Part No. 17; Page No. 346) that she said:
It was revealed in the Qur'an that ten clear sucklings prohibit marriage then it was abrogated (and substituted) by five clear sucklings, and the Prophet (peace be upon him) died while it was likewise.
One time of breast-feeding ends when the child leaves the breast to take a breath or to move. When he returns to the breast again, it will be considered as a second time of breast-feeding and so on. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.