The Wealth of Nations by Part 1 Chapter 6 Page 20

the rent of the first, the profit of the second, and the wages of the third. The whole, however, is commonly considered as the earnings of his labour. Both rent and profit are, in this case, confounded with wages.

As in a civilised country there are but few commodities of which the exchangeable value arises from labour only, rent and profit contributing largely to that of the far greater part of them, so the annual produce of its labour will always be sufficient to purchase or command a much greater quantity of labour than what employed in raising, preparing, and bringing that produce to market. If the society were annually to employ all the labour which it can annually purchase, as the quantity of labour would increase greatly every year, so the produce of every succeeding year would be of vastly greater value than that of the foregoing.