Imam al-Shafi'i (may Allah have mercy on him) says: We found the people of knowledge in general saying that the Messenger of Allah (peace and blessings be upon him) "fixed 100 camels upon the 'aqilah (paternal kin) for a free Muslim killed by mistake, and gave three years' respite for it, so that each year a third of the blood money is paid, in camels of specified ages."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16389