Sunan Ibn Majah, Volume 3, Book 21, Hadith 2649 (DarusSalam) ⓘ

It was narrated that Anas said: “Rubai, the paternal aunt of Anas, broke the tooth of a girl and they (her family) asked (the girl's family) to let her off, but they refused. They offered to pay compensatory money, but they refused. So they came to Prophet who ordered retaliation. Anas bin Nadr said: 'O Messenger of Allah, will the tooth of Rubai' be broken? By the One Who sent you with the truth, it will not be broken!' The Prophet said: 'O Anas, what Allah has decreed is retaliation.' So the people accepted that and forgave her. The Messenger of Allah said: 'there are among the slaves of Allah those who, if they swear by Allah, Allah fulfills their oath.'”

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى أَبُو مُوسَى، حَدَّثَنَا خَالِدُ بْنُ الْحَارِثِ، وَابْنُ أَبِي عَدِيٍّ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ كَسَرَتِ الرُّبَيِّعُ عَمَّةُ أَنَسٍ ثَنِيَّةَ جَارِيَةٍ فَطَلَبُوا الْعَفْوَ فَأَبَوْا فَعَرَضَ عَلَيْهِمُ الأَرْشَ فَأَبَوْا فَأَتَوُا النَّبِيَّ صلى الله عليه وسلم فَأَمَرَ بِالْقِصَاصِ ‏.‏ فَقَالَ أَنَسُ بْنُ النَّضْرِ يَا رَسُولَ اللَّهِ تُكْسَرُ ثَنِيَّةُ الرُّبَيِّعِ وَالَّذِي بَعَثَكَ بِالْحَقِّ لاَ تُكْسَرُ ‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ يَا أَنَسُ كِتَابُ اللَّهِ الْقِصَاصُ ‏"‏ ‏.‏ قَالَ فَرَضِيَ الْقَوْمُ فَعَفَوْا فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّ مِنْ عِبَادِ اللَّهِ مَنْ لَوْ أَقْسَمَ عَلَى اللَّهِ لأَبَرَّهُ ‏"‏ ‏.‏