Anas (may Allah be pleased with him) said: The sister of al-Rubayyi', Umm Harithah, wounded a person. The dispute came before the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) ruled: "There will be retaliation." Umm al-Rubayyi' said: O Messenger of Allah! Will retaliation be taken even from so-and-so? By Allah, never! The Prophet (peace and blessings be upon him) said: "Subhan Allah! Retaliation is indeed what is in the Book of Allah." She said: By Allah, retaliation can never be taken. She kept saying this until those people agreed to the blood money. Then he (peace and blessings be upon him) said: "How many of Allah's servants there are who, if they swear an oath by Allah, Allah fulfils their oath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16095