Vocabulary of the ḥadith:

• lā ḍarar (no harming): from the verb ḍarra yaḍurru, the opposite of benefiting, i.e., to bring harm upon someone. Ḍar (with a fatḥa) is the verbal noun, while ḍurr (with a ḍamma) is the name of the act. Its meaning here is: a man must not harm his brother by depriving him of any part of his right.
• wa-lā ḍirār (and no reciprocating harm): on the morphological pattern fiʿāl from the same root, meaning that one must not retaliate for a harm by inflicting something greater than what he suffered. The first term concerns initiating harm; the second concerns responding with an excessive counter-harm.

Points derived from the ḥadith:
1 – This ḥadith is one of the major legal maxims under which many situations and issues fall.
2 – The sense of “lā ḍarar” is the absolute prohibition of causing any corruption to others, whether private or public, and the obligation to ward off harm before it occurs by every feasible preventive measure. It also includes removing it after it occurs by whatever means are available.
3 – Consequently, the imposition of the lawful punishments on criminals does not contradict this maxim, even though it brings harm upon them, because those punishments realize justice and avert a broader and greater harm.
4 – The meaning of “wa-lā ḍirār” is the same harm motivated by vengeance that enlarges and expands the injury. Inflicting harm—even as retaliation—may not be intended for its own sake; it is resorted to only when necessary. The Law’s objective is to repel harm with no harm at all; if that is impossible, then with the least harm possible.
Thus, if someone destroys another person’s property, for example, it is not permissible to respond by destroying his property, for that merely broadens the harm without benefit. Rather, the preferred course is to oblige the offender to pay the value of what he destroyed, and that.