The Wealth of Nations by Part 1 Chapter 6 Page 3

and superior skill, are commonly made in the wages of labour; and something of the same kind must probably have taken place in its earliest and rudest period.

In this state of things, the whole produce of labour belongs to the labourer; and the quantity of labour commonly employed in acquiring or producing any commodity is the only circumstance which can regulate the quantity exchange for which it ought commonly to purchase, command, or exchange for.

As soon as stock has accumulated in the hands of particular persons, some of them will naturally employ it in setting to work industrious people, whom they will supply with materials and subsistence, in order to make a profit by the sale of their work, or by what their labour adds to the value of the materials.