Muwatta Malik, Book 39, Hadith 2 (USC-MSA)

Malik related to me that he had heard that Urwa ibn az-Zubayr and Sulayman ibn Yasar said, "The mukatab is a slave as long as any of his kitaba remains to be paid." Malik said, "This is my opinion as well." Malik said, "If a mukatab dies and leaves more property than what remains to be paid of his kitaba and he has children who were born during the time of his kitaba or whose kitaba has been written as well, they inherit any property that remains after the kitaba has been paid."

وَحَدَّثَنِي مَالِكٌ، أَنَّهُ بَلَغَهُ أَنَّ عُرْوَةَ بْنَ الزُّبَيْرِ، وَسُلَيْمَانَ بْنَ يَسَارٍ، كَانَا يَقُولاَنِ الْمُكَاتَبُ عَبْدٌ مَا بَقِيَ عَلَيْهِ مِنْ كِتَابَتِهِ شَىْءٌ ‏.‏ قَالَ مَالِكٌ وَهُو رَأْيِي ‏.‏ قَالَ مَالِكٌ فَإِنْ هَلَكَ الْمُكَاتَبُ وَتَرَكَ مَالاً أَكْثَرَ مِمَّا بَقِيَ عَلَيْهِ مِنْ كِتَابَتِهِ وَلَهُ وَلَدٌ وُلِدُوا فِي كِتَابَتِهِ أَوْ كَاتَبَ عَلَيْهِمْ وَرِثُوا مَا بَقِيَ مِنَ الْمَالِ بَعْدَ قَضَاءِ كِتَابَتِهِ ‏.‏

sunnah.com

also referenced under: Book 39, Hadith 1493 (In-Book)