Hasan al-Basri, Ibrahim al-Nakha'i, and al-Sha'bi (may Allah have mercy on them) say: If a slave woman is given one divorce and she is freed during her waiting period ('iddah), then her 'iddah will be that of a free woman and the husband will have the right to take her back. But if she is freed after two divorces, then her 'iddah will be that of a slave woman and the husband will not have the right to take her back.
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2444
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 1267، وابن أبى شيبة فى «مصنفه» برقم: 19117، 19118، 19121»