A recent news story reported that when a newly engaged woman gave some change to a homeless man, her ring fell into his coin jar. After he proceeded to return it, he received a large sum of money in donations from people touched by the story. This is an example of the

This story is an example of the just-world hypothesis or just-world fallacy.

Explanation:

According to the just-world hypothesis, a person is going to be rewarded if she or he performs a morally good act, and punished in case of performing a morally bad act. It comes from the belief that the world is fair and every action in the world has consequences. As a result, good people are rewarded, while bad people are punished.

Here, the homeless man returned the engagement ring (morally good act) and was received donations (reward for a morally good act).