… is from page 147 of Hayek’s 1967 collection, Studies in Philosophy, Politics, and Economics; specifically, it’s from his 1957 essay “What is ‘Social’? – What Does It Mean?” (emphasis added):
True service to the social concept is not rendered by the imposition of absolute authority or leadership, nor does it even consist of common endeavour towards a common aim, but rather of the contribution that each and every one of us makes to a process which is greater than any one of us, from which there constantly emerges something new, something unforeseen, and which can flourish only in freedom.
