Is it permissible to buy a gift for one's brother with charity money, or must it be bought with the giver's private money?

If your brother is wealthy, then buy him what he needs with gift money, not charity money, because the poor are more deserving of voluntary charity money. However, if your brother is poor, then he is more deserving of your charity than others, for the Prophet, peace and blessings be upon him, said: "Charity given to a poor person is one charity, but charity given to a relative is two: charity and strengthening of kinship ties."