I'll say it this way from now on

I've frequently made the point that when Person A accuses Person B of doing something immoral, the accusation is apt to tell you more about Person A than it does about Person B. And that is especially true when it's a blanket accusation: when somebody says, "It's not possible to hate the sin without hating the sinner," he gives you no real reason to think that conservative Christians can't love drug addicts without hating those addicts' addiction, but he does establish that, if for example he happens to think that you are a "homophobe," you may be uncomfortably confident that he hates you.

But today I heard this idea expressed with perfect pith...only I can't remember where. I'll happily give credit where it's due if somebody can tell me the original source of this quote:

"He who accuses the world convicts only himself."