Muwatta Malik, Book 43, Hadith 1584 (In-Book)

Yahya related to me from Malik from Hisham ibn Urwa that his father said, "The tribe is not obliged to pay blood-money for intentional murder. They pay blood-money for accidental killing."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّهُ كَانَ يَقُولُ لَيْسَ عَلَى الْعَاقِلَةِ عَقْلٌ فِي قَتْلِ الْعَمْدِ إِنَّمَا عَلَيْهِمْ عَقْلُ قَتْلِ الْخَطَإِ ‏.‏

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also referenced under: Book 43, Hadith 8 (USC-MSA)