Abu Hasan, the freed slave of Banu Nawfal, narrates that he asked Ibn Abbas (may Allah be pleased with them both) for a ruling about a slave who was married to a slave woman; he divorced her twice so that she was separated from him, and later both of them were freed. Is it permissible for the man to propose marriage to her again? Ibn Abbas (may Allah be pleased with them both) said: Yes, the Messenger of Allah (peace and blessings be upon him) judged in this way.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10769