Q. In regards to question 1831 above, where the collecting sheliach returned the coins given to him to the donor and he is allowed to accept them. Does he need now to give them now to another charity?
What kind of charity?
If one was approached by a tzedaka collector, and while he was looking for some change to give him, the collector left. Does the donor have to run after him since he had already decided what to give and acted accordingly? Does he have to donate that money to another charity?

A. Horav Shlomo Miller’s Shlit’a opinion is that the donor that took the coins back should indeed preferably donate them to another needy person.
However, the Rov maintains that one should always be “Mosser Modoah” or declare, preferably in front of the beis din when he makes hattoras nedorim or the annulment of past oaths, vows and pledges on Erev Rosh Hashana, that any future commitments and pledges done for charity, even done only on ones mind, should not be counted as a nedder or an oath. One can do that declaration any time and does not need be necessarily in front of a beis din or court of three.
When this declaration was done, and one finds it difficult to comply with the tzedaka he intended to give, he does not have to pursue and run after the collector he intended and acted to give charity to.
(See next question 1850).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a