Hadhrat Mufti Muhammad Shafi' Sahib [rh] said something in one of his speeches, which kept me pondering since I read it the first time (some weeks ago). I'll confine myself to a quick translation, because it's too late right now (3:00) to elaborate on my thoughts about it.

Islam has told such formulas for the economy, that if the philisophers of the whole world would ponder and research, they would be incapable of bringing up better guidelines. It's said, "Earn your estate through Halal ways and then let it not be spend in prohibited ways." On the one hand ways of earning and on the other ways of expending. The boundaries of both have been taught to the servants by Allah Ta'ala through the beloved Messenger .

Earning and Spending of Wealth

We've to realize, that the whole economical conduct basicly consists of two parts. First to acquire money, second to spend it. So, it's obvious that the means in terms of acquiring wealth are ikhtiyari [optional]. But acquiring wealth on it's own is ghayr-ikhtiyari [non-optional] and today we're obsessed with and indulged in the ghayr-ikhtiyari abondoning the ikhtiyari. Spending is a completely ikhtiyari act. Now, let's first of all take the acquiring of wealth. The farmer plows the earth. Then he spends time and money to sow seeds in the ground. Then he flushes. These are tools of acquiring wealth, which are optional. In the same way a shop-owner opens a shop, fills it with stuff and gets hold of stuff, that's capable of being sold on the market. These tools are optional, but too pull the money out of the customer's pocket is ghayr-ikhtiyari. There are ten shops of the same kind. From two the customer buys things and from two not. This is the sustenance of Allah Ta'ala, who puts in the heart of the customer to buy from such-and-such shop. This sustaining belongs to Allah Ta'ala, who brings the wheat out of the earth and flourishes this wheat by means of heat, cold, sunshine, rain, wind and all other means. And Allah Ta'alas common habit is to grant those, who do effort, the fruits of it. But He's capeable to if He wills fail someone despite all these tools and if He wills grant more outcome out of less tools and less means. That's why adopting means is ikhtiyari and to gain it's effects is ghayr-ikhtiyari.
[Excerpt from "Khutbaat Mufti-e-'Azam"]