… is from page 48 of the 2007 Definitive Edition (Bruce Caldwell, ed.) of F.A. Hayek’s classic 1944 volume, The Road to Serfdom ; specifically, it’s from Hayek’s Foreword to the 1956 American paperback edition:
The important point is that the political ideals of a people and its attitude toward authority are as much the effect as the cause of the political institutions under which it lives. This means, among other things, that even a strong tradition of political liberty is no safeguard if the danger is precisely that the new institutions and policies will gradually undermine and destroy that spirit.
Hayek  died 21 years ago today, less than seven weeks short of his 93rd birthday.