The Book of Oaths (qasamah), Retaliation and Blood Money
45/2. Chapter:
Qasamah
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ رَافِعٍ، قَالَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، قَالَ أَنْبَأَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنِ ابْنِ الْمُسَيَّبِ، قَالَ كَانَتِ الْقَسَامَةُ فِي الْجَاهِلِيَّةِ ثُمَّ أَقَرَّهَا رَسُولُ اللَّهِ صلى الله عليه وسلم فِي الأَنْصَارِيِّ الَّذِي وُجِدَ مَقْتُولاً فِي جُبِّ الْيَهُودِ فَقَالَتِ الأَنْصَارُ الْيَهُودُ قَتَلُوا صَاحِبَنَا .
It was narrated that Ibn Al-Musayyab said: "Qasamah existed during the Jahiliyyah, then the Messenger of Allah confirmed it in the case of an Ansari who was found slain in the dry well of the jews, and Ansar said: "The Jews kill our companion."'
Reference : Sunan an-Nasa'i 4709In-book reference : Book 45, Hadith 4English translation : Vol. 5, Book 45, Hadith 4713