Your Eminence, Sheikh: What is Qisas? And is it permissible to take revenge?

Qisas is killing in return for killing, and damaging a limb in return for damaging a limb. It is said, "The guardian of the slain retaliated against the killer (iqtassa)," meaning he exacted his qisas. And "The ruler exacted qisas from him (aqassahu)" means he fully implemented qisas upon him. The origin of the word is from "qassa al-athar" (he traced the footsteps), meaning he followed them, and "qassa al-hadeeth" (he narrated the discourse), meaning he narrated it exactly as it was, both of which imply following. And qisas is the following of an act with an act.