Sahih al-Bukhari, Wills and Testaments (Wasaayaa)
Book 55, Hadith 41
Narrated 'Abu 'Abdur-Rahman narrated:
When 'Uthman (ra) was circled (by the rebels), he looked upon them from above and said, "Ias you by Allah, I ask nobody but the Companions of the Prophet (pbuh), dont you know that Allah's Messenger (pbuh) 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 (i.e., 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 permissible.