penny for your thoughts

One day, as your ladyship was playing on the harpsichord to my master, Mr Jones was sitting in the next room, and methought he looked melancholy. La! says I, Mr Jones, what's the matter? a penny for your thoughts, says I.

1749, Henry Fielding, chapter XIV, in The History of Tom Jones, a Foundling, volume II, London: A[ndrew] Millar, […], →OCLC, book IV, page 106

As for Harry, he sate in very deep meditation over the scene; and when Mrs. Lambert offered him a penny for his thoughts, he said, “That he thought, Young Norval, Douglas, What-d'ye-call-'em, the fellow in white satin—who looked as old as his mother—was very lucky to be able to distinguish himself so soon.

1857–1859, W[illiam] M[akepeace] Thackeray, chapter LIX, in The Virginians. A Tale of the Last Century, volume (please specify |volume=I or II), London: Bradbury & Evans, […], published 1858–1859, →OCLC

And she said to Gerty: —A penny for your thoughts. —What? replied Gerty with a smile reinforced by the whitest of teeth.

1922 February 2, James Joyce, “[13]”, in Ulysses, Paris: Shakespeare and Company […], →OCLC

The penny-post is, commonly, an institution through which you seriously offer a man that penny for his thoughts which is so often safely offered in jest.

1854 August 9, Henry D[avid] Thoreau, “Where I Lived, and What I Lived For”, in Walden; or, Life in the Woods, Boston, Mass.: Ticknor and Fields, →OCLC

“A penny for your thoughts,” said Miss Wilkinson, looking at him with a smile. “I’m not going to tell you,” he answered. He was thinking that he ought to kiss her there and then.

1915, W[illiam] Somerset Maugham, chapter XXXIII, in Of Human Bondage, New York, N.Y.: George H[enry] Doran Company, →OCLC