Musannaf Ibn Abi Shayba 19:611

Abu Bakr narrated to us, he said: Isa ibn Yunus narrated to us, from Hanzala al-Sadusi, he said: I heard Anas ibn Malik saying: "An order would be given for a whip, and its tip would be cut off. Then it would be pounded between two stones until it became soft, and then [the person] would be struck with it." I said to Anas, "In whose time was this?" He said, "In the time of Umar ibn al-Khattab."