Agreement about Diya (blood money)

Narrated Anas:

Ar-Rabi, the daughter of An-Nadr broke the tooth of a girl, and the relatives of Ar-Rabi' requested the girl's relatives to accept the Irsh (compensation for wounds etc.) and forgive (the offender), but they refused. So, they went to the Prophet who ordered them to bring about retaliation. Anas bin An-Nadr asked, "O Allah";
Apostle! Will the tooth of Ar-Rabi' be broken? No, by Him Who has sent you with the Truth, her tooth will not be broken." The Prophet ﷺ said, "O Anas! Allah";
law ordains retaliation." Later the relatives of the girl agreed and forgave her. The Prophet ﷺ said, "There are some of Allah's slaves who, if they take an oath by Allah, are responded to by Allah i.e. their oath is fulfilled). Anas added, "The people agreed and accepted the Irsh."

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الأَنْصَارِيُّ، قَالَ حَدَّثَنِي حُمَيْدٌ، أَنَّ أَنَسًا، حَدَّثَهُمْ أَنَّ الرُّبَيِّعَ ـ وَهْىَ ابْنَةُ النَّضْرِ ـ كَسَرَتْ ثَنِيَّةَ جَارِيَةٍ، فَطَلَبُوا الأَرْشَ وَطَلَبُوا الْعَفْوَ، فَأَبَوْا فَأَتَوُا النَّبِيَّ ﷺ فَأَمَرَهُمْ بِالْقِصَاصِ. فَقَالَ أَنَسُ بْنُ النَّضْرِ أَتُكْسَرُ ثَنِيَّةُ الرُّبَيِّعِ يَا رَسُولَ اللَّهِ لاَ وَالَّذِي بَعَثَكَ بِالْحَقِّ لاَ تُكْسَرُ ثَنِيَّتُهَا فَقَالَ " يَا أَنَسُ كِتَابُ اللَّهِ الْقِصَاصُ ". فَرَضِيَ الْقَوْمُ وَعَفَوْا فَقَالَ النَّبِيُّ ﷺ " إِنَّ مِنْ عِبَادِ اللَّهِ مَنْ لَوْ أَقْسَمَ عَلَى اللَّهِ لأَبَرَّهُ ". زَادَ الْفَزَارِيُّ عَنْ حُمَيْدٍ عَنْ أَنَسٍ فَرَضِيَ الْقَوْمُ وَقَبِلُوا الأَرْشَ.