Musnad Abu Ya'la al-Mawsili 147:34

Abu Bakr ibn Abi Shaybah narrated to us, Muhammad ibn al-Hasan narrated to us, Muhammad ibn Sulaym narrated to us, from Najih Abu Ali, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace), Abu Bakr, and Umar performed stoning, and their command is a Sunnah.