The Wealth of Nations by Part 2 Chapter 4 Page 8

The stock lent by the three monied men is equal to the value of the goods which can be purchased with it, and is three times greater than that of the money with which the purchases are made. Those loans however, may be all perfectly well secured, the goods purchased by the different debtors being so employed as, in due time, to bring back, with a profit, an equal value either of coin or of paper. And as the same pieces of money can thus serve as the instrument of different loans to three, or for the same reason, to thirty times their value, so they may likewise successively serve as the instrument of repayment.

A capital lent at interest may, in this manner, be considered as an assignment from the lender to the borrowers of a certain considerable portion of the annual produce; upon condition that the borrower in return