Indirect reciprocity has been proposed to explain prosocial behavior among strangers, whereby the prosocial act is returned by a third party. However, what happens if the prosocial act cannot be observed by the third party? Here, we examine whether empathy serves as a clue for prosociality and whether people are more generous toward more empathetic people. In a laboratory study, we measured prosocial behavior as the amount sent in the dictator game and empathy based on the Interpersonal Reactivity Index (IRI). By using an incentivized task, we find that people believe that more empathetic participants send more money in the dictator game. Thus, people see empathy as a clue for prosocial behavior. Furthermore, in a second dictator game, participants indirectly reciprocate by sending more money to more empathetic recipients. Therefore, we suggest that empathy can replace a reputation derived from observable prosocial behavior in triggering indirect reciprocity.