Many to choose from, here's one of my favorites from Aristotle;
"Excellence is an art won by training and habituation. We do not act rightly because we have virtue or excellence, but we rather have those because we have acted rightly. We are what we repeatedly do. Excellence, then, is not an act but a habit.”
And from that you can extrapolate all matter of virtue and vice, i.e., a person can do an act of good, but that act doesn't then make that person good, rather merely a person that did a good thing. However, a person that falls into the habit of doing good things is becoming a good person. Conversely, a person that does a bad thing, isn't by necessity a bad person, but a person that did a bad thing, and if that person continues to do bad things, that person is becoming a bad person. I like the concept of repeated actions being the stick from which we are measured.