Musannaf Ibn Abi Shayba 13:1474

Abu Bakr narrated to us, he said: Ibn Fudayl narrated to us, from Ash'ath, from al-Sha'bi and al-Hakam, that they both said: If a man has a debt and a remainder of his *kitabah* (contract of manumission), he should look at what has become due upon him of his installments and what is for his creditors, then he should divide that according to the shares.