Musannaf Ibn Abi Shayba 18:1150

Abu Bakr narrated to us, he said: Yahya bin Sa'id narrated to us, from Sufyan, from Firas, from al-Sha'bi, from Masruq, that he divided the blood money (diyah) into sevenths: four parts for three (groups/categories) and three parts for four (groups/categories).