Assalaamu alaykum. If one's father gives him some money to use as his own and he donates it, who will obtain the reward?
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
The money that the father gives to his son as a gift becomes the son's personal property once he takes it into his possession. He is entitled to dispose of this money freely as he wishes by means of spending in charity, offering a gift, and the like of the lawful ways of disposing of money, provided that the son is legally competent to dispose of money as per the Shariah, namely that he is adult and sane. The exception in this case is when the father sets a condition for the gift stipulating that it must be spent in a certain way or for a certain purpose. In this case, the son has no right to dispose of this gift in any other way or for any other purpose other than that specified by the father; the Prophet, sallallahu ‘alayhi wa sallam, said, "Muslims are bound by their conditions." [At-Tirmithi and others - Al-Albaani graded it saheeh (sound)]
Maalik related in his book Al-Muwatta' that Al-Qaasim ibn Muhammad said, "I have only come upon people who abide by the conditions made regarding their property and what they are given." Yahya said that he heard Maalik say, "This is also the stance that we adopt."
If the father has not stipulated any condition, the son has the right to dispose of the money for any lawful purpose that he wishes. If he spends this money in charity, he earns the reward for it. The father earns the reward for offering his son this gift of money and helping him do good.
Allah knows best.