Division of labour is generally associated with Adam Smith (1776). The concept of division of labour attains significance because it helps in formulating an endogenous growth model, along with the extent of the market. The idea is that specialization has a positive effect on the extent of the market, which in turn leads to more division of labour.
Apart, from this, in everyday life, we come across division of labour in various shapes and sizes. A very strong example of this is that of outsourcing. Earlier, physicians attended to a patient and they were quite knowledgeable in many aspects of medicine. Now, we have ENT specialists, paediatricians, cardiologists, nephrologists, neurologists, orthopaedicians, etc. This is visible in the IT industry as well. And specialization has not left academic untouched either. Within economics, one finds econometricians, economic historians, experimental economists, macroeconomists and so on.
In the Wealth of Nations, Smith  talks of pin-making to illustrate division of labour:
“One man draws out the wire, another straights it, a third cuts it, a fourth points it, a fifth grinds it at the top for receiving the head; to make the head requires two or three distinct operations; to put it on, is a peculiar business, to whiten the pins is another; it is even a trade by itself to put them into the paper; and the important business of making a pin is, in this manner, divided into about eighteen distinct operations, which, in some manufactories, are all performed by distinct hands, though in others the same man will sometimes perform two or three of them.” [p. 15]
Today, while going through Sir William Petty’s ‘Another Essay in Political Arithmetick Concerning the Growth of the City of London‘ which was published in 1682, I found division of labour mentioned. Petty illustrates it using the example of watch-making:
“In the making of a Watch, If one Man shall make the Wheels, another the Spring, another shall Engrave the Dial-plate, and another shall make the Cases, then the Watch will be better and cheaper, than if the whole Work be put upon any one Man.” [p. 473]
Then, while going through the Campbell and Skinner edited Volume of Wealth of Nations, I noticed that in the first foot note, they refer to Petty as probably being the first modern author to talk about division of labour.
Interesting to know that William Petty, hailed by Marx has the first political economist, had developed notions of division of labour!