It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) "forbade the earnings of slave-women."
It is possible that what is meant by this prohibition is the slave-woman who is a prostitute, just as it is reported from Sayyiduna Abu Mas'ud al-Ansari (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) forbade the earnings of a prostitute, and from Sayyiduna Rafi' bin Khadij (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The earnings of a prostitute are foul."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإجارة / 11687