Stand firm against evil thoughts, for if you fail to do so, they will become ideas, if you do not, they will become desires, so fight against them. If you do not, they will become a form of determination and intention, if you do not resist, they will become actions, and if you do not follow them up with their opposite, they will become habits that will be hard to quit.
(Imam Ibn Al-Qayyim – Al-Fawa’Id – A Collection Of Wise Sayings pg 54. )
The heart is healthy ONLY when it is functioning contrast to its desires. In other words, desires are the sickness of the heart and opposing them is the cure.
Ibn al-Qayyim, Sins & their Punishments
621. Narrated Anas bin Malaik (radhi Allaahu anhu) : Allaah’s Messenger (Sallallaahu Alaihi Wasallam) said,
The son of Adam (i.e.,man) grows old and so also two (desires) grow old with him, (and they are); love for wealth and (a wish for) a long life.”
[Saheeh Al-Bukhaari, Hadeeth No. 430, Vol. 8]
Source : The Book Of Zakat : Chapterr 38 – Dislikeness of the longing for worldly possessions.
Al-Lulu Wal-Marjan,Compiled by : Fuwad Abdul-Baqi,Translated by : Dr. Muhammad Muhsin Khan
Abu Al-Hasan Ali bin Ahmad said:
“Deal with optional acts of worship as if they are obligatory, and acts of disobedience as if they are kufr (disbelief), and your desires as if they are poison, and socializing with the people as if it were fire, and nurturing of your soul as if it were medicine.”
Khilasat Al-Athaar, 3/401