Musnad Abu Ya'la al-Mawsili 2:12

Abu Khaythama narrated to us, Sufyan ibn 'Uyayna narrated to us, from al-Zuhri, from 'Ubayd Allah, from Ibn 'Abbas, who said: When the sun passed its zenith, 'Umar ascended the pulpit and the callers to prayer gave the call. He then delivered a sermon, praised Allah, and extolled Him. He said in his sermon: "Stoning is a truth for the married person if there is clear evidence, or pregnancy, or confession. The Messenger of Allah (peace and blessings of Allah be upon him) stoned, and we stoned with him and after him."