Musannaf Ibn Abi Shayba 18:1332

Abu Bakr narrated to us, he said: Humayd ibn Abd al-Rahman narrated to us, from Musa ibn Abi al-Furat: That Umar ibn Abd al-Aziz said: "Whichever slave kills a slave intentionally, then kill him for him, and the price of the first [slave]— Take it out from the public treasury (Bayt al-Mal) and give it to his masters."