Know, then, that those whom laziness has overcome find it difficult to carry out spiritual struggle, to discipline and purify the self, and to refine their character. They wrongly believe that because natures do not undergo change, it is not possible to change character traits. If this were the case, then counsels, admonitions and discipline would be of no use. How can it not be possible to change the behavior of humans, when it is clear that it is possible to change the behavior of animals such as eagles, dogs, and horses by training?
In reality, those that deny that character traits can be changed have confused changing traits with removing them. What is not possible is the second. If one sought to completely remove all traces of anger and passion, it would not be possible. However it is possible to control and direct them through spiritual struggle and discipline, which we have been commanded to do so, and these are the means of our salvation and the path to reach Allah. At the same time, dispositions vary. Some are quick to change, others, slow.
(Uthmani, Imam Zafar Ahmed (tran:Faraz Rabbani) 2004. Sufism and Good Character. California: White Thread Press)