The Prophet (peace and blessings be upon him) forbade taking back a gift. He said: “The one who takes back his gift is like the dog which vomits then goes back to its vomit. And we (believers) should not act according to this bad example.” (Al-Bukhari and Muslim)
Dr. Monzer Kahf, a prominent economist and counselor, stated: The ruling is that once a donation is handed out, even if not spent yet by the recipient, it becomes final and the donor has no right whatsoever to ask for it back. The recipient, mosque or otherwise, must not give it back.
On the other hand, if the former donor is presently in need for help from Zakah of charity, he/she may be given in accordance with needs and priorities of the Islamic organization that runs the zakah fund/charity. It is of course very good to help those who helped charitable causes when they were better off.