Literally, virtue is its own punishment
in Latin. Pronounced VEER-tus POY-na SOO-ah ESST.
This statement, sometimes known as Denniston's Law but also attributed to Aneurin Bevan, is not the same as "no virtuous action will go unpunished". What it says to me is that when one is virtuous, one is punishing oneself by not taking the actions that would not be virtuous.
I, not wanting to be a glutton, refuse to eat a rich dessert after dinner. Therefore, I have punished myself for not wanting to be a glutton by depriving myself of the enjoyment of the dessert.
It is worthwhile noting that most fat and sugar substitutes are based around the idea that this can be avoided.
Why translate it into Latin, then? That way it sounds more profound.