He traced it back to the Prophet ﷺ, who said, "Whoever is killed in a blind feud or out of partisan zeal, by a stone, a whip, or a stick, the blood-money owed for him is that of accidental killing. Whoever kills deliberately, retaliation is due. And whoever stands between the killer and retaliation, upon him is the curse of Allah, the angels, and all people. No turning aside nor ransom will be accepted from him."
حدثنا محمد بن معمر حدثنا محمد بن كثير حدثنا سليمان بن كثير عن عمرو بن دينار عن طاوس
رفعه إلى النبي ﷺ قال من قتل في عمية أو عصبية بحجر أو سوط أو عصا فعليه عقل الخطإ ومن قتل عمدا فهو قود ومن حال بينه وبينه فعليه لعنة الله والملائكة والناس أجمعين لا يقبل منه صرف ولا عدل
Its isnad is sahih. Nasai narrated it in the chapter on Qasamah, the section on whoever kills with a stone or a whip, Hadith 4794, from Muhammad bin Muamar with this chain, and Abu Dawud narrated it, Hadith 4540, from the hadith of Sulayman with this chain.