Al-Zuhri (may Allah have mercy on him) said: In the time of the Messenger of Allah (peace and blessings be upon him) the diyah was 100 camels, one uqiyah for each camel, which came to 4000 dirhams. When the time of Sayyiduna Umar (may Allah be pleased with him) came, and camels became expensive and silver cheap, Sayyiduna Umar (may Allah be pleased with him) fixed 2 uqiyahs of silver for each camel, which came to 8000 dirhams. Then camels kept becoming more expensive and silver cheaper, until Sayyiduna Umar (may Allah be pleased with him) fixed 12000 dirhams, or 1000 dinars, or 200 cows, or 2000 goats.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16173