Bhagavad Gita, Chapter 2, Verse 38

Treating pleasure and pain, gain and loss, victory and defeat alike, engage then in battle. So you will not incur sin.

Do it because it's yours to do, not because you're chasing one outcome over another. That's what keeps it clean.

The instruction isn't just to act, it's to act without being pulled around by whether things go well or badly. Duty carried out like that doesn't leave the kind of residue that selfish action does.