Sister's son

By blood, a sister's son is the male blood child of a blood sister, in three kinds: of a full sister, of a paternal sister and of a maternal sister. By fostering, he is the male child a blood sister suckled. The word child covers male and female; the word son covers only the male. ¹

The jurists agree that he is a mahram kinsman among those with blood-ties through a female, so the rules of mahrams apply to him, including the prohibition of marriage and the permission for women to enter upon him. They agree that he is among those with blood-ties through a female, with rules in inheritance, maintenance, the right to lead the funeral prayer and guardianship. They differ on whether the maternal aunt comes before the father in the custody of her sister's son. ^{1 2}

The Encyclopedia says the detailed rules are treated in their places in the books of fiqh, and refers the rules on those with blood-ties through a female to its entry on kinship (arham). ²