Jami` at-Tirmidhi Book 17, Hadith 24
"Ali gave a Khutbah, and said: 'O people, establish the penalties upon your slaves, those married from them and those unmarried. A slave girl of the Prophet (ﷺ) committed illegal sexual intercourse so he ordered me to whip her. I went to her and she was just experiencing her post-natal bleeding, so I feared that if I were to whip her I would kill her' - or he said: 'She would die' - 'so I went to the Messenger of Allah (ﷺ) and I told that to him. So he said: 'You did well.'"
That the Messenger of Allah (ﷺ) said: "If one of your slave girl commits illegal sexual intercourse, then whip her three times according to the Book of Allah, and if she does it again then sell her, even if it is for a rope made of hair."
That the Messenger of Allah (ﷺ) implemented the penalty by beating forty times, with two shoes - Mis'ar (one of the narrators) said: "It think it was for wine."