Sayyiduna Ali (may Allah be pleased with him) said: If a slave kills a free man, he will be handed over to the heirs of the slain man; if they wish they may kill him, and if they wish they may spare him. Al-Shaykh said: If they choose to spare him and want the blood money, he is to be sold to pay the blood money of the slain man. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15961