It is narrated from Hazrat Saeed bin Musayyib (may Allah have mercy on him): Such a slave-girl, after being freed, will observe the waiting period (‘iddah) of a free woman, and the husband will have the right to take her back. After the completion of the ‘iddah, if he wishes, he can marry her.
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2445
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 1268، وابن أبى شيبة فى «مصنفه» برقم: 19120»