A believer never enjoys his sin, never finds his delight completed. Rather, even while committing the sin his heart is faced with grief, though the intoxication of desire covers up his feeling of it.
If the heart ever becomes void of this remorseful ache and the joy of sinning overpowers any feeling of remorse, then one should doubt one's faith, and cry over the death of his heart.
Were the heart alive, the committing of sin would make it sad, upbraid and constrict it, and it would sense it.
A wound, after all, does not cause pain to a corpse.
[ Madarij al-Salikin ] Ibn Qayyim al-Jawzi