Mishkat al-Masabih #3419

Aba Huraira told that he heard the Prophet say, "When the slave woman of any of you commits fornication and the matter is clear, he should give her the appropriate beating, but not hurl reproaches at her. If she does it again he should give her the appropriate beating, but not hurl reproaches at her. If she does it a third time and the matter is clear he should sell her, even if only for a rope of hair." (Bukhari and Muslim)