Musannaf Ibn Abi Shayba 9:238

Abū al-Ḥasan, a freed slave of the Banū Nawfal, said: "I and my wife were slaves, and I divorced her twice. Then we were emancipated after that, and I wanted to take her back. So I asked Ibn ʿAbbās, and he said: 'If you take her back, she is with you upon one [remaining] divorce, and two have passed. The Messenger of Allah (ﷺ) decreed that.'"