The Wealth of Nations by Part 1 Chapter 6 Page 16

of making by the use of the money. Part of that profit naturally belongs to the borrower, who runs the risk and takes the trouble of employing it; and part to the lender, who affords him the opportunity of making this profit. The interest of money is always a derivative revenue, which, if it is not paid from the profit which is made by the use of the money, must be paid from some other source of revenue, unless perhaps the borrower is a spendthrift, who contracts a second debt in order to pay the interest of the first. The revenue which proceeds altogether from land, is called rent, and belongs to the landlord. The revenue of the farmer is derived partly from his labour, and partly from his stock.

To him, land is only the instrument which enables him to earn the wages of this labour, and to make the profits of this stock.