Is it permissible for a father to give a specific item to one of his children while excluding the others?

Question:
A man has four children, one of whom is an employee, married, and has five children. Part of the money in his father's possession is savings from the salary of the aforementioned son. It is known that this son is providing for the maintenance of his children, his parents, and his siblings, as they all live in one house. His father wishes to donate one-fifth of the money in his possession to the aforementioned son in return for his work and income.

Answer:
It is established from the Prophet (peace and blessings be upon him) that he said: It is agreed upon that it is authentic. Therefore, a father may not give a specific item to one of his children to the exclusion of the others, except with the consent of the remaining children who are of legal age and sound mind, according to the most correct of the scholars' opinions. However, if he wishes to treat what he received from his salary in the future as a loan to him, or as a trust in his possession, there is no harm in that. He must clarify this in a valid document, thereby preserving for him the right to the income that came to him, or part of it, and not having given him anything, but rather having preserved his own money for him. And Allah knows best.