Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated from the Messenger of Allah (peace and blessings of Allah be upon him), he (peace be upon him) said: "Any slave woman who gives birth to a child from her master, she will be free after his (the master's) death."
Hadith Referenceمسند اسحاق بن راهويه / كتاب العتق و المكاتب / 483
Hadith Takhrij«سنن ابن ماجه ، كتاب العتق ، باب امهات الاولاد ، رقم : 2515 . سنن كبري بيهقي ، رقم : 346/10 . اسناده ضعيف .»