Musnad Ahmad 928:27

Abdullah narrated to us, Khalaf ibn Hisham narrated to us, Hammad ibn Zayd narrated to us, from Asim ibn Bahdalah, from Zirr, who said: Ubayy ibn Ka'b said to me: "How many [verses] do you read Surah al-Ahzab? Or how many do you count it?" I said to him: "Seventy-three verses." He said: "Is that all? I have certainly seen it, and it was equivalent to Surah al-Baqarah. And we used to read in it: 'The old man and the old woman, if they commit adultery, then stone them both absolutely, as a deterrent from Allah, and Allah is All-Mighty, All-Wise.'"