It is narrated from Sayyiduna Rafi' bin Khadij (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) "forbade the earnings of a slave-woman until it is known where she earned it from."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإجارة / 11690