Qasamah existed during the Jahiliyyah and the Messenger of Allah approved of it as it had been during the Jahiliyyah, and he ruled accordingly among some of the Ansar concerning a victim whom they claimed the Jews of Khaibar had Killed. (Sahih) Ma'mar contradicted the two of them.
Sunan an-Nasa'i Book 45, Hadith 3
← Previous Hadith the Messenger or Allah approved of Qasamah as it had been during the Jahiliyyah.

Sunan an-Nasa'i Book 45, Hadith 2 Next Hadith → "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."'

Sunan an-Nasa'i Book 45, Hadith 4