‘How many kinds of livings that people earn and deal with each other are there? What are the ways of expenses?’ a man asked Imam as-Sadiq (‘as), who answered:
All the livings that people earn and deal with each other are four.
‘Are all these legal? Are they all illegal? Or are some legal and some illegal?’ asked the man.
The Imam (‘as) answered:
These four kinds may be legal from one side and illegal from another. These kinds are known and familiar. First of all, there is work in governmental offices. The first of this kind is the jobs of the rulers down to the least job of individuals. Then comes the trade including all sorts of deals, such as vending and purchase. Then come the industries along with all of their kinds. Then come the contracts of lease. All these kinds are legal from one side and illegal from another. God’s obligation on servants is to follow and practice the legal forms of these kinds only and avoid the illegal.