It was narrated from Anas that:

the sister of Ar-Rubai' Umm Harithah injured a person and they referred the dispute to the Messenger of Allah. The Messenger of Allah said: "Retaliation, retaliation (Qisas)." Umm Ar-Rabi said: 'O Messenger of Allah, how could retaliation be carried out against so and so? No, by Allah, retaliation willnever be carried out against her!' The Messenger of Allah said: "Subhan Allah, O Umm Ar-Rabi'! decreed by Allah." She said: "No, by Allah, retaliation will never be carried out against her!" And she carried on until they accepted Diyah (blood money). He (the prophet) said: "There are among the slaves of Allah who, if they swear by Allah, Allah fulfills their oath.

أَخْبَرَنَا أَحْمَدُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا عَفَّانُ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، قَالَ حَدَّثَنَا ثَابِتٌ، عَنْ أَنَسٍ، أَنَّ أُخْتَ الرُّبَيِّعِ أُمَّ حَارِثَةَ، جَرَحَتْ إِنْسَانًا فَاخْتَصَمُوا إِلَى النَّبِيِّ ﷺ فَقَالَ رَسُولُ اللَّهِ ﷺ " الْقِصَاصَ الْقِصَاصَ " . فَقَالَتْ أُمُّ الرُّبَيِّعِ يَا رَسُولَ اللَّهِ أَيُقْتَصُّ مِنْ فُلاَنَةَ لاَ وَاللَّهِ لاَ يُقْتَصُّ مِنْهَا أَبَدًا . فَقَالَ رَسُولُ اللَّهِ ﷺ " سُبْحَانَ اللَّهِ يَا أُمَّ الرُّبَيِّعِ الْقِصَاصُ كِتَابُ اللَّهِ " . قَالَتْ لاَ وَاللَّهِ لاَ يُقْتَصُّ مِنْهَا أَبَدًا . فَمَا زَالَتْ حَتَّى قَبِلُوا الدِّيَةَ . قَالَ " إِنَّ مِنْ عِبَادِ اللَّهِ مَنْ لَوْ أَقْسَمَ عَلَى اللَّهِ لأَبَرَّهُ " .