… is from page 91 of Frank Knight‘s 1956 collection, On the History and Method of Economics; specifically, it is from Knight’s 1928 essay “Historical and Theoretical Issues in the Problem of Modern Capitalism” (citation excluded; emphasis added):
It is not at all to the point to say, as [Werner] Sombart and the Germans regularly do, that no one could be so stupid as not to know the difference between money and wealth, that the ancient fable of Midas is enough to dispel this illusion from any mind. Certainly the mercantilists did not identify the two explicitly (though they came close enough to that at many points), but it is just as unquestionable that only on the basis of such a premise can any sort of sense be made out of the great bulk of mercantilistic utterances or policies. And why should it be otherwise? Conditions are no different today in most of the civilized capitalistic world. The man from Mars reading the typical pronouncement of our best financial writers or statesmen could hardly avoid the conclusion that a nation’s prosperity depends upon getting rid of the greatest possible amount of goods and avoiding the receipt of anything tangible in payment for them.