Nafi' (may Allah have mercy on him) narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both) that he had a mukatab who had children from a slave woman of his. He had paid 15 thousand of his kitabah, then he died. So Ibn Umar took possession of his wealth, gave nothing to the children, made the children slaves, and took possession of his wealth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21685