The Messenger of Allah ﷺ said, "You name your killer, then you swear fifty oaths against him, and he will be handed over to you."
أن رسول الله ﷺ قال: تسمون قاتلكم، ثم تحلفون عليه خمسين يمينا فتسلمه إليكم.
Ibn Abu Asim narrated it in the chapter on blood money (259), and this is his wording. Ahmad (16096) and Bayhaqi (8/126) also narrated it, all of them through the report of Muhammad bin Ishaq, who said, "Zuhri told me, from Sahl bin Abu Hathma," then he related it, and the wording found in the two of them is longer. Its chain is hasan because of Muhammad bin Ishaq.Rulings on the oath procedure1. The next of kin of the slain begin with the oaths of the oath procedure. This is the view of Malik, Shafii, and Ahmad. Abu Hanifa said that those sought for the killing, meaning the defendants, begin instead, based on the established principle, "Your witnesses, or else his oath," meaning the oath of the defendant.2. The oath procedure applies only to the crime of killing, not to other kinds of assault.3. If the next of kin of the slain take the oath, retaliation becomes obligatory in the case of intentional killing, and blood money becomes obligatory in cases of quasi-intentional or accidental killing, according to Malik and Ahmad. According to Abu Hanifa and Shafii, blood money is obligatory in all cases, due to the uncertainty in establishing the killing.4. The oath procedure applies only when the killer is unknown. If he is known, then retaliation or blood money becomes obligatory, according to the Hanafis. According to the majority, it applies when the killer is known but the evidence is not sufficient to prove the killing.5. The oath procedure applies only when the slain person is found in a locality where there is religious or worldly enmity, or when the victim names the killer, or when a man bearing traces of blood is found near the victim, or when a single witness testifies against the killer. There is disagreement regarding some of these conditions.6. If the slain person is found in a public place such as a garden, a street, or a masjid, then there is no oath procedure in this case.For more, see Minna Kubra (7/131), which contains many details relating to these matters.