What is the ruling on one who harms himself for the sake of Allah?

Harm and hardship in worship can be legitimate or illegitimate. The legitimate kind is that which results from an act commanded by Islamic law, such as someone who single-handedly charges the enemy for the benefit of the Muslims, or performing ghusl in extreme cold. Such a person is a doer of good. The illegitimate kind is that which is not commanded by Islamic law, to the point of self-destruction, such as fasting that leads to perishing; this is impermissible. Allah’s pleasure is not in merely afflicting oneself, but rather the reward is commensurate with the benefit of the action. Deeds vary in merit according to what is achieved in the hearts. Hardship is not intended for its own sake, but the reward for it is because worship necessitates it, and because of the legitimate benefits that result from it. The intent of the Sacred Law is not hardship, but rather the well-being of the servants. What accompanies hardship, like bitter medicine, aims for healing. Thus, the believer is rewarded for enduring harm resulting from obedience to Allah, not for intentionally seeking hardship itself.