Musannaf Ibn Abi Shayba 13:1469

Abu Bakr narrated to us, he said: Hafs narrated to us, from al-Shaybani, Ash'ath, and Isma'il, from al-Sha'bi, from Shurayh, regarding a *mukattab* (an enslaved person with a contract of manumission) who died while he had debt and a remainder of his *kitabah* (contractual payments) remaining. He said: His masters shall be included [in the distribution of the estate] for what has become due of his installments. And Hammad said: They shall be included for what has become due and what has not become due.