Sahih Bukhari, Chapter: Wills and Testaments (Wasaya)

When Uthman was circled(by the rebels), he looked upon them from above and said, "I ask you by Allah, I ask nobody but the companions of the Prophet (SAW), don't you know that Allah's Messenger said, 'Whoever will (buy and) dig the well of Ruma will be granted paradise,' and I (bought and) dug it? Don't you know that he said, 'Whoever equip the army of Usra (Tabuk's Ghazwa) will be granted paradise,' and I equipped it?" They attested whatever he said. When Umar founded his endowment he said, "Its administrator can eat from it." The management of the endowment can be taken over by the founder himself or any other person, for both cases are permissable.