Virtue is its own reward
Definition 1 of 1
Pro Tip 1/3Self-Rewarding
Understanding that the phrase implies you feel good doing right things without needing external praise. 
He returned the lost wallet without expecting a thank-you, feeling that virtue is its own reward.
Pro Tip 2/3Idiomatic Usage
Recognize it's an idiomatic expression meaning the value of virtue is internal, not external. 
Even when others didn't notice her charitable acts, she knew virtue is its own reward.
Pro Tip 3/3Non-Materialistic
It conveys a non-materialistic value, suggesting that the moral satisfaction is more important than material rewards. 
She volunteers for the love of community, feeling virtue is its own reward, not for any financial gain.