وَحَدَّثَنِي عِيسَى بْنُ حَمَّادٍ الْمِصْرِيُّ، أَخْبَرَنَا اللَّيْثُ، عَنْ سَعِيدِ بْنِ أَبِي سَعِيدٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّهُ سَمِعَهُ يَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏"‏ إِذَا زَنَتْ أَمَةُ أَحَدِكُمْ فَتَبَيَّنَ زِنَاهَا فَلْيَجْلِدْهَا الْحَدَّ وَلاَ يُثَرِّبْ عَلَيْهَا ثُمَّ إِنْ زَنَتْ فَلْيَجْلِدْهَا الْحَدَّ وَلاَ يُثَرِّبْ عَلَيْهَا ثُمَّ إِنْ زَنَتِ الثَّالِثَةَ فَتَبَيَّنَ زِنَاهَا فَلْيَبِعْهَا وَلَوْ بِحَبْلٍ مِنْ شَعَرٍ ‏"‏ ‏.‏

Abu Huraira reported that he heard Allah's Messenger (PBUH) as saying: When the slave-woman of any of you commits adultery and this (offence of hers) becomes clear, she should be flogged (as the prescribed) punishment, but hurl no reproach at her. If she commits adultery again, she should (again be punished) by flogging, but hurl no reproach upon her. If she commits fornication for the third time and it becomes clear, then he should sell her, even if only for a rope of hair. Translation Not Available

Book reference: Sahih Muslim Book 29 Hadith 4219
Web reference: Sahih Muslim Book 17 Hadith 1703 a