حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ الْمُكَاتَبُ عَبْدٌ مَا بَقِيَ عَلَيْهِ مِنْ كِتَابَتِهِ شَىْءٌ ‏.‏

Malik related to me from Nafi that Abdullah ibn Umar said, "Amukatab is a slave as long as any of his kitaba remains to be paid." Translation Not Available

Book reference: Muwatta Imam Malik Book 39 Hadith 1492
Web reference: Muwatta Imam Malik Book 39 Hadith 1