Narrated Ibn `Abbas: The law of Qisas (i.e. equality in punishment) was prescribed for the children of Israel, but the Diya (i.e. blood money was not ordained for them). So Allah said to this Nation (i.e. Muslims): "O you who believe! The law of Al-Qisas (i.e. equality in punishment) is prescribed for you in cases of murder: The free for the free, the slave for the slave, and the female for the female. But if the relatives (or one of them) of the killed (person) forgive their brother (i.e. the killers something of Qisas (i.e. not to kill the killer by accepting blood money in the case of intentional murder)----then the relatives (of the killed person) should demand blood-money in a reasonable manner and the killer must pay with handsome gratitude. This is an allevitation and a Mercy from your Lord, (in comparison to what was prescribed for the nations before you). So after this, whoever transgresses the limits (i.e. to kill the killer after taking the blood-money) shall have a painful torment." (2.178)

Narrated Anas: The Prophet said, "The prescribed Law of Allah is the equality in punishment (i.e. Al-Qisas)." (In cases of murders, etc.)

Narrated Anas: That his aunt, Ar-Rubai' broke an incisor tooth of a girl. My aunt's family requested the girl's relatives for forgiveness but they refused; then they proposed a compensation, but they refused. Then they went to Allah's Messenger and refused everything except Al-Qisas (i.e. equality in punishment). So Allah's Apostle passed the judgment of Al-Qisas (i.e. equality of punishment). Anas bin Al-Nadr said, "O Allah's Messenger! Will the incisor tooth of Ar-Rubai be broken? No, by Him Who sent you with the Truth, her incisor tooth will not be broken." Allah's Messenger said, "O Anas! The prescribed law of Allah is equality in punishment (i.e. Al-Qisas.)" Thereupon those people became satisfied and forgave her. Then Allah's Messenger said, "Among Allah's Worshippers there are some who, if they took Allah's Oath (for something), Allah fulfill their oaths."