Abu Juhayfah says: I said to Sayyiduna Ali (may Allah be pleased with him): "O Commander of the Believers! Do you have anything special from revelation?" He said: "Nothing at all. By the One who split the seed and created the soul, (there is nothing) except the understanding that Allah grants to a person, and what is in this scroll." I asked: What is in the scroll? He said: "(Rulings) about blood-money and the freeing of captives, and that 'a believer shall not be killed in retaliation for a polytheist.'" Then he says: I asked Mutarrif: What is freeing the captive? He said: That he be freed from the enemy; the Sunnah has run in this way. And Mutarrif says that al-'aql means paying blood-money.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18828