Musnad Ahmad 25:529

Sa'd ibn Ibrahim narrated to us, my father narrated to us, from Muhammad ibn Ishaq, Dawud ibn al-Husayn narrated to me, from 'Ikrimah, the freed slave of Ibn 'Abbas, from Ibn 'Abbas, who said: "Rukanah ibn 'Abd Yazid, brother of the Banu al-Muttalib, divorced his wife three times in a single sitting, and he grieved over her intensely. He said: The Messenger of Allah, peace and blessings of Allah be upon him, asked him: 'How did you divorce her?' He said: I divorced her three times. He said: 'In a single sitting?' He said: Yes. He said: 'That is only one, so take her back if you wish.'" He said: So he took her back. And Ibn 'Abbas used to hold the view that divorce is only at every period of purity.