Musnad Ahmad 1153:352

Yunus narrated to us, Laith narrated to us, from Yazid ibn Abi Habib, from Ammar ibn Abi Farwah, that Muhammad ibn Muslim narrated to him, that Urwah narrated to him, that Amrah bint Abd al-Rahman narrated to her, that Aisha narrated to her, that the Messenger of Allah, peace and blessings of Allah be upon him, said: "If the slave woman commits adultery, then flog her. And if she commits adultery, then flog her. And if she commits adultery, then flog her. Then sell her, even if for a rope." And the *dhafir* (rope) is the rope.