It is not permissible to designate one of the children for inheritance

Question: A girl inherited money from her father, and he allocated the entire inheritance to her, excluding her brother. He also made a bequest regarding that money and forbade his daughter from giving her brother any of this money after his death. However, after the father passed away, the sister took pity on her brother and appointed him as her agent over the entire inheritance, including the bequest, so that he could manage his affairs, because he is weak, has dependents, and has no money. This son was involved in an accident, and it was said that he lost part of his mind. The son denied that he had taken any money from his sister; he neither returned the money nor carried out his father's bequest. Is there any blame on me for disobeying my father's bequest if I give my brother the entire inheritance to dispose of as he sees fit, despite my father's refusal of that? May Allah reward you with good.

Answer: It is not permissible for a Muslim to allocate a portion of the estate to some of his heirs in excess of their right, based on the saying of the Prophet (peace and blessings be upon him): Therefore, it is obligatory to divide the estate between them according to the division prescribed by Allah. If there are other heirs with them, each is given his right. If there is a dispute in the matter, it is referred to the court. And success is from Allah.