Musannaf Ibn Abi Shaybah 21800 — A mukatab is a slave as long

Sulayman bin Yasar says: I sought permission to visit Sayyidah Aishah (may Allah be pleased with her). She asked: "Is it Sulayman?" I said: "Yes, it is Sulayman." Sayyidah Aishah (may Allah be pleased with her) asked: "Have you paid the kitabah payment of your masters that remained due from you?" I said: "Yes, a little of it remains." She said: "Then come in, for as long as even a little of the kitabah payment remains due from you, you are still a slave."