2. Al-Baqara (The Cow)

Surah: 2   Aya: 178

178. Ya ayyuha allatheena amanoo kutiba AAalaykumu alqisasu fee alqatla alhurru bialhurri waalAAabdu bialAAabdi waalontha bialontha faman AAufiya lahu min akheehi shay-on faittibaAAun bialmaAAroofi waadaon ilayhi bi-ihsanin thalika takhfeefun min rabbikum warahmatun famani iAAtada baAAda thalika falahu AAathabun aleemun
  

  Translation

178. O you who believe! Al-Qisâs (the Law of Equality in punishment) is prescribed for you in case of murder: the free for the free, the slave for the slave, and the female for the female. But if the killer is forgiven by the brother (or the relatives, etc.) of the killed against blood money, then adhering to it with fairness and payment of the blood money, to the heir should be made in fairness. This is an alleviation and a mercy from your Lord. So after this whoever transgresses the limits (i.e. kills the killer after taking the blood money), he shall have a painful torment.