Abu al-Janub al-Asadi said: A Muslim man who had killed a dhimmi was brought to Ali (may Allah be pleased with him). He (may Allah be pleased with him) had ordered that he be killed when his brother came and said: I have forgiven his blood. Ali (may Allah be pleased with him) asked: Were you not forced into this? He said: No. Killing him will not bring my brother back. They gave me the blood money and I am content. Ali (may Allah be pleased with him) said: You know that whoever is under our protection, his blood and his blood money are like ours.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15934