… is from page 236 of Ludwig von Mises‘s 1958 essay “Economic Freedom in the Present-Day World,” reprinted as Chapter 47 in the Bettina Bien Greaves edited volume Economic Freedom and Interventionism:
Earlier ages had labored under the misapprehension that no man or group of men can profit but by the loss of others. In entirely demolishing this fallacy, 18th-century social philosophy and economics paved the way for the unprecedented achievements of modern Western civilization.