Suppose a Gabbai Tzedakah passes our good friend Reuven while making his collection rounds. Reuven reaches into his pocket for his wallet and removes the money he wants to donate. By the time Reuven lifts his eyes, the Gabbai is gone.

What should Reuven now do with the money he separated for Tzedakah? Is he allowed to keep it? Can he give it to some other Tzedakah?