It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) and Zaid bin Khalid (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) was asked about a slave girl: What is the ruling if an unmarried one commits fornication? He (peace and blessings be upon him) said: "If she commits fornication, flog her. If she commits fornication again, flog her. Then if she commits fornication again, flog her again. Then sell her, even if it is for a rope." Ibn Shihab (may Allah have mercy on him) says: I do not know whether he (peace and blessings be upon him) ordered her to be sold for a rope after the third or fourth time she committed fornication, and «ضَفِير» means a rope.
Hadith Referenceالسنن المأثورة / باب الحدود / 529
Hadith Takhrijصحیح بخاری، البیوع، باب بیع العبد الزانی، رقم: 2154، صحیح مسلم، الحدود، باب رجم الیہود ..... الخ، رقم: 1703