He traced it back to the Prophet ﷺ, who said, "Whoever is killed in a blind quarrel or a tribal feud, by a stone, a whip, or a stick, then the blood-money owed for him is that of accidental killing. Whoever is killed deliberately, the punishment is retaliation. Whoever stands in the way of that, upon him is the curse of Allah, the angels, and all people, no obligatory or voluntary act will be accepted from him."
رفعه إلى النبي ﷺ قال: من قتل في عمية، أو عصبية بحجر أو سوط أو عصا فعليه عقل الخطأ. ومن قتل عمدا فهو قود، ومن حال بينه وبينه فعليه لعنة الله والملائكة والناس أجمعين لا يقبل منه صرف ولا عدل.
Nasai (4790) and Ibn Majah (2635) both narrated it from Muhammad bin Muamar, who said, "Muhammad bin Kathir narrated to us," who said, "Sulayman bin Kathir narrated to us, from Amr bin Dinar, from Tawus, from Ibn Abbas," and he related it. Its chain of transmission is sahih, for Muhammad bin Kathir, that is, Abdi Basri, though he is among the narrators found in all the major collections, Ibn Main said of him, "He was not trustworthy." Saeed bin Sulayman corroborated him, narrating from Sulayman bin Kathir. Abu Dawud (4540) and Nasai (4789) narrated it as a raised hadith with the same wording, except that Abu Dawud did not give the wording of the hadith itself, but instead referred to the hadith of Sufyan, from Amr bin Dinar, from Tawus, who said, "The Messenger of Allah ﷺ said," and related the hadith. He did not mention in it the cursing of the angels, and moreover Sufyan's narration is disconnected (mursal), but the first narration, being a raised and connected one, strengthens the narration of Muhammad bin Kathir.As for his saying, "ummiyyah," in Abu Dawud's version it appears as "umyaa," with the ain vowelled with kasrah and the meem doubled. Khattabi said, "Umyaa is on the pattern of faeelaa, from blindness, just as one says between them there was 'ramyaa,' meaning throwing. Its meaning is that a group throws things at one another and a dead man is found among them, with no knowledge of who killed him, and the matter remains obscure and unclear, so in this case the blood money is due."As for his saying, "whoever kills deliberately, retaliation is due against him," meaning qisas, "and whoever stands between him and it," meaning between the killer and the retaliation, and prevents the guardians of the slain from carrying out retaliation after they have demanded it, not by seeking pardon from them, for that is permissible, indeed commendable.