قال ابن القيم رحمه الله
المؤمن لا تتم له لذة بمعصية أبداً، ولا يكمل بها فرحه، بل لا يباشرها
إلا والحزن مخالط لقلبه، ولكن سُكر الشهوة يحجبه عن الشعور به .
ومتى خلِي قلبه من هذا الحزن واشتدت غبطته وسروره
فليتهم إيمانه، وليبك على موت قلبه
فإنه لو كان حياً لأحزنه ارتكابه للذنب، وغاظه وصعب عليه،
ولا يحس القلب بذلك، وحيث لم يحس به فما لجرح بميت إيلام.
رحم الله الإمام
The real believer never enjoys a sin, and the sin doesn't please him while he is doing it as much as it makes him feel with sadness and regret, however the effect of the lust prevents that feeling temporarily though
and whenever his heart does't feel with that sadness and feels instead with joy by doing that sin, then it is his faith to blame, and he should cry for declaring the sign of the death of his heart, as if his heart was really alive, he would have felt with sadness and regret instead... and as his heart wasn't able to feel with sorrow for that sin.. then an injury wouldn't hurt a dead heart anyway.
Says Ebn Al Qayem,
May Allah bless and mercy his soul