Jami` at-Tirmidhi Book 17, Hadith 25
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."
"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 a man who had drunk wine was brought to the Prophet (ﷺ), so he beat him about forty times with two stalks of a palm tree. So Abu Bakr did similarly, and by the time 'Umar became Khalifah he sought council from the people. And 'Abdur-Rahman bin 'Awf said: 'I see that the lightest penalty is eighty lashes,' so 'Umar ordered that.