Ar-Rubai (the paternal aunt of Anas bin Malik) broke the incisor tooth of young Ansari girl. Her family demanded the Qisas and they came to the Prophet ﷺ who passed the judgment of Qisas. Anas bin An-Nadr (the paternal uncle of Anas bin Malik) said, "O Messenger of Allah ﷺ! By Allah, her tooth will not be broken." The Prophet ﷺ said, "O Anas! (The law prescribed in) Allah's Book is Qisas." But the people (i.e. the relatives of the girl) gave up their claim and accepted a compensation. On that Allah's Apostle said, "Some of Allah's worshippers are such that if they take an oath, Allah will fulfill it for them."  

كَسَرَتِ الرُّبَيِّعُ وَهْىَ عَمَّةُ أَنَسِ بْنِ مَالِكٍ ثَنِيَّةَ جَارِيَةٍ مِنَ الأَنْصَارِ فَطَلَبَ الْقَوْمُ الْقِصَاصَ فَأَتَوُا النَّبِيَّ ﷺ فَأَمَرَ النَّبِيُّ ﷺ بِالْقِصَاصِ فَقَالَ أَنَسُ بْنُ النَّضْرِ عَمُّ أَنَسِ بْنِ مَالِكٍ لاَ وَاللَّهِ لاَ تُكْسَرْ سِنُّهَا يَا رَسُولَ اللَّهِ فَقَالَ رَسُولُ اللَّهِ ﷺ يَا أَنَسُ كِتَابُ اللَّهِ الْقِصَاصُ فَرَضِيَ الْقَوْمُ وَقَبِلُوا الأَرْشَ فَقَالَ رَسُولُ اللَّهِ ﷺ إِنَّ مِنْ عِبَادِ اللَّهِ مَنْ لَوْ أَقْسَمَ عَلَى اللَّهِ لأَبَرَّهُ