What should the son do with the amount he borrowed from his wealthy father before his death, knowing that this amount represents a significant portion of his inheritance share? Should he deduct it from the inheritance and give it in charity, or donate everything he inherited from his father because it is more than the loan amount?

The borrowed money is a debt owed by the son to his father, and it is part of the inheritance. If the son is the sole heir, then the money is an inheritance for him to dispose of as he wishes. It is good for him to give it as charity on behalf of his father, or make it an endowment, or spend it on himself, his children, and his relatives, in accordance with the Hadith of Jabir: "Begin with yourself and give charity to it; if anything remains, then for your family; if anything remains from your family, then for your relatives..." However, if there are other heirs, they share with him in the money that is owed by him. It is then added to the estate and divided among all the heirs, or deducted from the share of the borrowing son. It should not be given as charity or put into a charitable project because it is a right for all heirs. Issues of inheritance should be referred to Sharia courts to ensure the rights of all heirs, debts, and bequests.