Kitáb-i-Aqdas

Question: Is it necessary that the brother, in order to qualify for his portion of the inheritance, be descended from both the father and the mother of the deceased, or is it sufficient merely that there be one parent in common?

Answer: If the brother be descended from the father he shall receive his share of the inheritance in the prescribed measure recorded in the Book; but if he be descended from the mother, he shall receive only two thirds of his entitlement, the remaining third reverting to the House of Justice. This ruling is also applicable to the sister.