Source
Charles Marshall, Shattering the Glass Slipper: Destroying Fairy-tale Thinking Before It Destroys You (2003), approx. p. 142
Editorial Note
Despite its ubiquity on quote pages and social media under C. S. Lewis's name, this line appears nowhere in his published books, essays, letters, or recorded talks, and both the C. S. Lewis Foundation and Lewis scholar William O'Flaherty (author of The Misquotable C.S. Lewis) flag it as one of the most common false attributions to him. The aphorism is a condensed paraphrase of a passage from motivational speaker Charles Marshall's 2003 book Shattering the Glass Slipper, which reads at greater length that integrity is doing the right thing when no one else is looking or will ever know and there will be no recognition for it—wording Marshall presents as his own, not a quotation of another author. Lewis does explore a kindred idea in Mere Christianity, arguing that right actions done for the wrong reason build no real virtue, which likely explains why the pithier modern maxim later drifted onto his name. Because a specific, documented non-Lewis origin can be named, this is a misattribution rather than merely an unsourced saying; note the neat one-sentence form is itself a paraphrase, not a verbatim line even from Marshall.