Al-Qasim bin Abi Bazzah (may Allah have mercy on him) said: A Muslim killed a dhimmi in Syria, and the case came before Sayyiduna Abu Ubaydah bin al-Jarrah (may Allah be pleased with him). He wrote to Sayyiduna Umar (may Allah be pleased with him) about it, and Sayyiduna Umar (may Allah be pleased with him) wrote back: If he is a habitual criminal, then kill him; otherwise impose four thousand as blood money.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15930