Sayyiduna Anas (may Allah be pleased with him) said: Sayyidah Rubayyi' bint al-Nadr (may Allah be pleased with her) broke the front tooth of a girl. Her family offered them compensation (arsh), but they refused; then they asked them to forgive, but they refused, and the case came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) ordered retaliation (qisas). Meanwhile her brother, Sayyiduna Anas bin al-Nadr (may Allah be pleased with him), came and said: O Messenger of Allah! Will Rubayyi's tooth also be broken? By Allah! That cannot be. The Prophet (peace and blessings be upon him) said: "O Anas! The decree of Allah is that there be retaliation." Meanwhile the claimants agreed to forgive, and he (peace and blessings be upon him) said: "There are some among the servants of Allah who, if they swear by Allah, Allah fulfils their oath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15883