In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Imaam Ibnul Jawzi [rahimahullaah] said: Know that desires [i.e. the desires that violate the commands, prohibitions and pure Islamic principles] can overcome a person in the different fields of study, exits him from the confines of sound reasoning and enters him into behaviour that is tantamount to madness [or folly]. It might enter affairs of knowledge and thus leads a person to oppose that which sound knowledge commands, and it might enter Zuhd [i.e. abstinence from those permissible things of the worldly life which one can do without] and thus leads him to Riyaa [i.e. he abstains out of showing off so that he is regarded a pious person].
[Dhammul Hawaa’ page 38. Slightly paraphrased]