The ruling on a child taking the surplus of his father's money and an explanation of the hadith "You and your wealth belong to your father"

Question:
May Allah reward you. Honorable Shaykh, Muhammad, a thousand times from al-Kharj, says: My father sends me to buy things for you and gives me, for example, one hundred riyals or more, while the cost is seventy riyals. I take the rest without his knowledge, even though he does not ask me. What is the meaning of the hadith "You and your wealth belong to your father," or is there a condition for that? What?

Answer:
It is not permissible for you to take the remainder of the money he gave you to buy a need from the profits unless he gives you permission to do so. However, it is not permissible for him to give you something without your brothers, so he must not single you out for a gift without your brothers. Therefore, two things are required: first, that he gives permission, and second, that he treats your brothers in the same manner. Otherwise, it is obligatory for you to safeguard your actions and return the remainder to your father.
As for his saying (peace and blessings be upon him), "You and your wealth belong to your father," this is a calculation for the husband.
[The speaker is] a slave of the child, and the father addressed the Messenger (peace and blessings be upon him) with the words, "Fear Allah and be just between your children." He said to him, "Did you not give this to [the other child]?" He said, "No." He said, "Fear Allah and be just between your children." His saying (peace and blessings be upon him), "You and your wealth, O my son, I am the book of your children." Allah the Exalted says: Question and the child is from the effort of his father. And he said (peace and blessings be upon him), "Your children are from your earnings. The best of what you have earned is your children, and your children are from your earnings." It is permissible for the father to take from his child's wealth what does not harm the child or what the child needs.