Musnad Ahmad 2:116

Hashim narrated to us, [he said] Shu'ayb informed us, from 'Ubayd Allah ibn 'Abd Allah ibn 'Utbah ibn Mas'ud, [he said] 'Abd Allah ibn 'Abbas informed me, [he said] 'Abd al-Rahman ibn 'Awf narrated to me: That 'Umar ibn al-Khattab addressed the people, and he heard him saying: "Beware, for there are people who say: 'What is the matter with the stoning [penalty]? In the Book of Allah, it is the lashing!' Yet the Messenger of Allah (may Allah bless him and grant him peace) stoned, and we stoned after him. And were it not that people might say, or speakers might speak: 'That 'Umar added to the Book of Allah that which is not from it,' I would have inscribed it as it was revealed."