Found this...

Rereading one of my books. I liked it. It's from "The Runelords", by David Farland. The character making the statement is known as Days, his position as part of an order of men dedicated to chronicling the lives of important people.

""Men who believe themselves to be good, who do not search their own souls, most often commit the worst atrocities. A man who sees himself as evil will restrain himself. It is only when we do evil in the belief that we do good that we pursue it wholeheartedly. ... I'm glad you question yourself. Men don't become good by performing an occasional kindly deed. You must constantly reexamine your thoughts and acts, question your virtue."