Musnad Ahmad 5:154

Husayn ibn Muhammad narrated to us, Shu'bah narrated to us, from Salamah and al-Mujalid, from al-Sha'bi, that they both heard him narrating: That when Ali stoned the woman from the people of Kufa, he flogged her on Thursday and stoned her on Friday. And he said: "I flog her according to the Book of Allah, and I stone her according to the Sunnah of the Prophet of Allah, may Allah bless him and grant him peace."