Musannaf Ibn Abi Shayba 33:1154

Yazid ibn Harun narrated to us, he said: Al-Hajjaj ibn Abi Zaynab informed us, he said: I heard Abu Uthman saying: "There is no verse in the Quran more hopeful to me for this nation than His saying: 'And others who have acknowledged their sins; they had mixed a righteous deed with another that was bad.'"