It is narrated from Hazrat Abu Saeed Khudri (may Allah be pleased with him) that during the blessed era of the Prophet (peace and blessings be upon him), we used to sell umm walad (slave women who had borne children).
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 11164
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف كسابقه .