Abu Juhaifah (may Allah have mercy on him) says that I asked Sayyiduna Ali (may Allah be pleased with him): "Do you have any knowledge from the Prophet besides the Qur'an?" He replied: "No, by Him who split the grain and created the soul, except that Allah grants understanding of His Book to a man, or this written document." I asked, "What is in this document?" He said: "It contains matters of blood money, the freeing of captives, and that no Muslim will be killed in retaliation for a disbeliever."
Hadith Referenceالسنن المأثورة / باب عقل الجنين / 600
Hadith Takhrijصحیح بخاری، العلم، باب كتابة العلم، رقم: 111۔