… is from page 48 of the 1969 Arlington House edition of Ludwig von Mises’s 1944 Yale University Press book, Omnipotent Government: The Rise of the Total State and Total War (available free-of-charge on-line here):
The essential teaching of liberalism is that social coöperation and the division of labor can be achieved only in a system of private ownership of the means of production, i.e., within a market society, or capitalism. All the other principles of liberalism – democracy, personal freedom of the individual, freedom of speech and of the press, religious tolerance, peace among the nations – are consequences of this basic postulate. They can be realized only within a society based on private property.