… is from page 363 of Karl Popper’s June 1947 speech “Utopia and Violence,” as this speech is reprinted in Popper’s 1963 collection – dedicated to F.A. Hayek – Conjectures and Refutations: The Growth of Scientific Knowledge:
The true rationalist, by contrast, will always know how little he knows, and he will be aware of the simple fact that whatever critical faculty or reason he may possess he owes to intellectual intercourse with others. He will be inclined, therefore, to consider men as fundamentally equal, and human reason as a bond which unites them. Reason for him is the precise opposite of an instrument of power and violence; he sees it as a means whereby these may be tamed.