Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: When a slave woman bears a child to her master, and after that she is married off and bears children, her children have the same status as her, as slaves, for as long as her master lives. If he dies, they are free.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب عتق أمهات الأولاد / 21800
Isma'il narrates from Amir (may Allah have mercy on him) that the children of a mudabbarah (a slave woman to be freed on her master's death) and the children of an umm walad have the same status (as their mothers): when their mothers are freed, their children are also freed, when the master dies.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب عتق أمهات الأولاد / 21801
Ibrahim (may Allah have mercy on him) said: The children of a mudabbarah and of an umm walad have the same status as their mothers.
(b) Umar bin Abd al-Aziz (may Allah have mercy on him) said, (concerning) a man who married his umm walad to a slave and she had children: they have the same status as their mother.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب عتق أمهات الأولاد / 21802