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 (ﷺ) and refused everything except Al-Qisas (i.e. equality in punishment). So Allah's Messenger (ﷺ) passed the judgment of Al-Qisas (i.e. equality of punishment). Anas bin Al-Nadr said, "O Allah's Messenger (ﷺ) ! 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 (ﷺ) 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 (ﷺ) said, "Among Allah's Worshippers there are some who, if they took Allah's Oath (for something), Allah fulfill their oaths."

حَدَّثَنِي عَبْدُ اللَّهِ بْنُ مُنِيرٍ، سَمِعَ عَبْدَ اللَّهِ بْنَ بَكْرٍ السَّهْمِيَّ، حَدَّثَنَا حُمَيْدٌ، عَنْ أَنَسٍ، أَنَّ الرُّبَيِّعَ، عَمَّتَهُ كَسَرَتْ ثَنِيَّةَ جَارِيَةٍ، فَطَلَبُوا إِلَيْهَا الْعَفْوَ فَأَبَوْا، فَعَرَضُوا الأَرْشَ فَأَبَوْا، فَأَتَوْا رَسُولَ اللَّهِ صلى الله عليه وسلم وَأَبَوْا إِلاَّ الْقِصَاصَ، فَأَمَرَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِالْقِصَاصِ، فَقَالَ أَنَسُ بْنُ النَّضْرِ يَا رَسُولَ اللَّهِ، أَتُكْسَرُ ثَنِيَّةُ الرُّبَيِّعِ لاَ وَالَّذِي بَعَثَكَ بِالْحَقِّ لاَ تُكْسَرُ ثَنِيَّتُهَا‏.‏ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ يَا أَنَسُ كِتَابُ اللَّهِ الْقِصَاصُ ‏"‏‏.‏ فَرَضِيَ الْقَوْمُ فَعَفَوْا، فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّ مِنْ عِبَادِ اللَّهِ مَنْ لَوْ أَقْسَمَ عَلَى اللَّهِ لأَبَرَّهُ ‏"‏‏.‏