It is narrated from Sayyiduna Zayd bin Khalid al-Juhani and Abu Hurayrah (may Allah be pleased with them both); they said: The Messenger of Allah (peace and blessings be upon him) was asked about a slave woman who is unmarried, and he (peace and blessings be upon him) said: "When she commits adultery, flog her; then if she commits adultery a third or a fourth time (al-Zuhri was in doubt), sell her, even if for a rope of hair."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5182