Musnad Ahmad 25:1229

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Yahya ibn Abi Kathir, from 'Umar ibn Mu'attib, from the freed slave of Banu Nawfal—meaning Abu al-Hasan—who said: Ibn 'Abbas was asked about a slave who divorced his wife with two pronouncements, then they were both emancipated; may he remarry her? He said: "Yes." It was said: On whose authority? He said: "The Messenger of Allah, may Allah bless him and grant him peace, issued a fatwa regarding that." 'Abd Allah said: My father said: It was said to Ma'mar: "O Abu 'Urwah, who is this Abu Hasan? You have indeed carried a great rock."