Sunan an-Nasa'i 4720
It was narrated from 'Amr bin Shu'aib, from his father, from his grandfather, that:
the younger son of Muhayysah was found slain one morning at the gate of one morning at the gates of Khaibar. The Messenger of Allah said: "Bring two witnesses to (say) who killed him, and he will hand him over to you." He said: "O Messenger of Allah, where shall I get two witnesses? He was found slain in the morning at their gates." He said: "Will you swear fifty oaths?" He said: "O Messenger of Allah, how can I swear concerning something I do not know?" The Messenger of Allah said: "Then will you accept fifty oaths from them?"  He said: "O Messenger of Allah, how can we accept their oaths when they are Jews?" So the Messenger of Allah told them (the Jews) to pay the Diyah and he would help them with half."
أَخْبَرَنَا مُحَمَّدُ بْنُ مَعْمَرٍ، قَالَ حَدَّثَنَا رَوْحُ بْنُ عُبَادَةَ، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ الأَخْنَسِ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ ابْنَ مُحَيِّصَةَ الأَصْغَرَ، أَصْبَحَ قَتِيلاً عَلَى أَبْوَابِ خَيْبَرَ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَقِمْ شَاهِدَيْنِ عَلَى مَنْ قَتَلَهُ أَدْفَعْهُ إِلَيْكُمْ بِرُمَّتِهِ ‏"‏ ‏.‏ قَالَ يَا رَسُولَ اللَّهِ وَمِنْ أَيْنَ أُصِيبُ شَاهِدَيْنِ وَإِنَّمَا أَصْبَحَ قَتِيلاً عَلَى أَبْوَابِهِمْ قَالَ ‏"‏ فَتَحْلِفُ خَمْسِينَ قَسَامَةً ‏"‏ ‏.‏ قَالَ يَا رَسُولَ اللَّهِ وَكَيْفَ أَحْلِفُ عَلَى مَا لاَ أَعْلَمُ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ فَنَسْتَحْلِفُ مِنْهُمْ خَمْسِينَ قَسَامَةً ‏"‏ ‏.‏ فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ نَسْتَحْلِفُهُمْ وَهُمُ الْيَهُودُ فَقَسَمَ رَسُولُ اللَّهِ صلى الله عليه وسلم دِيَتَهُ عَلَيْهِمْ وَأَعَانَهُمْ بِنِصْفِهَا ‏.‏