… is from page 233 of F.A. Hayek’s 1961 speech “The Moral Element in Free Enterprise,” which is reprinted as chapter 16 in Hayek’s 1967 collection, Studies in Philosophy, Politics, and Economics  (spelling typo corrected):
We want the individual to have liberty because only if he can decide what to do can he also use all his unique combination of information, skills and capacities which nobody else can fully appreciate. To enable the individual to fulfill his potential we must also allow him to act on his own estimates of the various chances and probabilities. Since we do not know what he knows, we cannot decide whether his decisions were justified; nor can we know whether his success or failure was due to his efforts and foresight, or to good luck. In other words, we must look at results, not intentions or motives, and can allow him to act on his own knowledge only if we also allow him to keep what his fellows are willing to pay him for his services, irrespective of whether we think this reward appropriate to the moral merit he has earned or the esteem in which we hold him as a person.