Musnad Ahmad 32:2084

'Affan narrated to us, Hammad ibn Salamah narrated to us, he said: Thabit informed us, from Anas, that the sister of Ar-Rabi' Umm Harithah wounded a person, so they disputed before the Messenger of Allah, peace and blessings of Allah be upon him. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Retaliation, retaliation." Umm Ar-Rabi' said: "O Messenger of Allah, shall retaliation be taken from so-and-so? No, by Allah, it shall never be taken from her." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Glory be to Allah, O Umm Ar-Rabi', the Book of Allah." She said: "No, by Allah, it shall never be taken from her." He said: So she did not cease until they accepted the blood money from her. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, among the servants of Allah are those who, if they were to swear by Allah, He would fulfill it for them."