Virtue does not seek a reward. Because then it has a motive, it is selfish. Virtue is selfless. It seeks nothing. Virtue is its own reward.
When you work for a cause, do you work for applause ? Then your cause is not fully pure. Virtue works for a cause with no expectation in return. Virtue is its own reward.
Virtue finds great inner satisfaction. Nobody external can match this inner fulfillment. You can't give a prize to virtue and fill it with joy. Virtue is its own reward.