Aesop's Fables (1884)
190. The Madman who Sold Wisdom.
A Madman once set himself up in the market place, and with loud cries announced that he would sell Wisdom. The people at once crowded about him, and some gave him gold for his wares, but they each got only a blow on the ear and a bunch of thread, and were well laughed at by their companions. One of them, however, took it more seriously than the others, and asked a wise sage what it meant. "It means," said the sage, "that if one would not be hurt by a Madman, he must put a bunch of thread over his ears." So the Madman was really selling Wisdom.
Aesop's Fables: A New Revised Version From Original Sources (translator not identified), 1884 . Illustrations by Ernest Henry Griset (1844-1907), John Tenniel (1820-1914) and Harrison Weir (1824-1906). Available online at Project Gutenberg.