Surat Al-'Isrā' - سورة الإسراء

وَلَا تَقْتُلُوا النَّفْسَ الَّتِي حَرَّمَ اللَّهُ إِلَّا بِالْحَقِّ ۗ وَمَن قُتِلَ مَظْلُومًا فَقَدْ جَعَلْنَا لِوَلِيِّهِ سُلْطَانًا فَلَا يُسْرِف فِّي الْقَتْلِ ۖ إِنَّهُ كَانَ مَنصُورًا

Muhsin Khan: And do not kill anyone which Allah has forbidden, except for a just cause. And whoever is killed (intentionally with hostility and oppression and not by mistake), We have given his heir the authority [(to demand Qisas, Law of Equality in punishment or to forgive, or to take Diya (blood money)]. But let him not exceed limits in the matter of taking life (i.e he should not kill except the killer only). Verily, he is helped (by the Islamic law).