https://en.m.wikisource.org/wiki/The_Wealth_of_Nations
It doesn't hurt to consider Ricardo as well.
From Ricardo, we get the Iron Law of Wages, and the Law of Rent. Key to understand is that these move in opposite directions:
* Wages tend to the minimum subsistence level, all else equal.
* Rent rises to claim the surplus value afforded.
That is, wages are based on the input costs, whilst rent is based on the output value (use value). The third element, price (sometimes "exchange value"), is what's at question.
(I distinguish cost, value, and price as three distinct concepts. This is a long-standing question, and in my view, a grossly confused one, in economics. They're related, but not deterministically. In the long term, C <= P < V. Bentham's "utility" is an exceptionally red herring. More, very much in development: https://redd.it/48rd02)
Note that this means that rent is determined by the pricing behaviour. If you're a "business owner" but you're not capable of extracting rents, you're either selling commodities or labour, you're not collecting rent. The term here is in the sense of economic rent. Simply "owning a business", without the economic circumstances which give rentier power, isn't sufficient -- don't confuse what it is you're doing with the systemic construct in which you're doing it. Weiderquist emphasises this point specifically, several commenters here clearly haven't grasped it.
Another elided discussion: rents are associated with access control, and can be thought of as authority over some (virtual or physical) gate. They're a natural element of any networked structure, in which nodes and links exist, most especially where some nodes have higher value, or control more flows. I believe though can't yet show that all cases of rent involve a fundamentally networked structure, again, virtual or real. My concern is that this may be a reflexive definition, I'm trying to determine that it is or isn't.
Another element of this is compensation for labour. Smith lays out five elements determining this, and I find them durable and comprehensive. In the Widerquist's case, the combination of requisite skills, and comparative unattractiveness, of teaching in Qatar, allow him to claim both a high wage and favourable working conditions (including a lighter-than-typical workload). This falls straight out of Smith. That is, he earns his salary "by doing a job few others are both willing and able to do".
If you're looking at the macro view, realise that these don't scale. That is, the innate and acquired capabilities to teach at University level are not widely distributed through the workforce, and the lack of appeal of various sorts of work is sufficient to dissuade (or prevent, or disqualify) others from taking part in it.
There are other elements here as well: the complimentarity of time and skills, on the one hand, with money, on the other (the classic business partnership). Tax structures (and who they benefit). The relationship of wealth and political power. Smith again: "Wealth, as Mr Hobbes says, is power." One of the shortest and clearest sentences in WoN, incidentally.