Mishkat al-Masabih 17 Prescribed Punishments كتاب الحدود 9

وَعَنْ أَبِي هُرَيْرَةَ قَالَ: سَمِعْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: «إِذَا زَنَتْ أَمَةُ أَحَدِكُمْ فَتَبَيَّنَ زِنَاهَا فَلْيَجْلِدْهَا الحدَّ وَلَا يُثَرِّبْ عَلَيْهَا ثمَّ إِنْ زنَتْ فلْيجلدْها الحدَّ وَلَا يُثَرِّبْ ثُمَّ إِنْ زَنَتِ الثَّالِثَةَ فَتَبَيَّنَ زِنَاهَا فَلْيَبِعْهَا ولوْ بحبْلٍ منْ شعرٍ»

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)