Musannaf Ibn Abi Shayba 26:425

Ya'la narrated to us, from Yahya ibn Sa'id, from Isma'il ibn Abi Hakim, that Umar ibn Abd al-Aziz emancipated a Christian slave of his. Then he (the slave) died, so he (Umar) placed his inheritance in the public treasury (Bayt al-Mal).