Abu Salamah narrates from Nufay' (may Allah have mercy on him), who was a slave and had a free woman as his wife. He gave her two divorces, and he asked Sayyiduna Uthman and Sayyiduna Zayd (may Allah be pleased with them both). They both said: Your divorce is the divorce of a slave, and her iddah is the iddah of a free woman.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرجعة / 15162