I'm afraid this is another one of those popular quotes that was never actually said by the author. It's spread around in various forms on the internet. It might have been a bad translation or a butchery of this sections of Politics: http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0058%3Abook%3D5%3Asection%3D1310a

But in this section, Aristotle is speaking about how both oligarchies and democracies are deteriorated by the dominant group doing what they want and how self-discipline is needed in the state as well as the individual, "for to live in conformity with the constitution ought not to be considered slavery but safety ". He says that democracies are defined by their liberty and the sovereignity of the people, but if liberty is defined as doing whatever you want, without self-discipline, liberty will be destroyed in the state. So in that way, he is sort of getting at what the quote says, but it is a fake quote and a butchery of what he's trying to say here.