Jihad against the lower self precedes jihad against external enemies and is the basis for it. Indeed, if one does not strive against himself first to do what he has been commanded and avoid what he has been forbidden and to wage war against it for the sake of Allah, one cannot possibly strive against external enemies. How can one strive against his enemies and be just if his enemy within has overpowered him, dominated him, and he did not strive or wage war against it for the sake of Allah? Rather, he cannot go out against his enemies unless he gives precedence to striving against himself.
— IBN QAYYIM AL-JAWZIYYA