"A physician is not angry at the intemperance of a mad patient; nor does he take it ill to be railed at by a man in fever: just so should a wise man treat all mankind, as a physician does his patient, and look upon them only as sick and extravagant, let their words and actions, whether good or bad, go equally for nothing, attending still his duty even in the coarsest offices that may conduce to their recovery" - Seneca, "Of Anger"
And thanks to Google's e-book library, you can read the entire book this quote is from - Seneca's Morals by Way of Abtract: To Which is Added a Discourse Under the Title of an Introduction - online, if you're so inclined. And here's the specific page this quote came from.
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