Hazrat Ibn Masood (may Allah be pleased with him) says that if a slave gives his slave-wife two divorces, and then both of them become free, she is not lawful for him until she marries another husband.

Ibrahim says that if a slave woman is married to a slave man, then he divorces her, and then both are freed together, she does not become lawful for him until she marries another husband.

16911 - And Abu Ma'shar from Ibrahim regarding a slave woman who is married to a slave man, and he divorces her twice, and then both are set free, (they said): She is not lawful for him until she marries another husband.

Hazrat Aamir says that if a slave woman is married to a slave man, then he divorces her, and then both are freed together, she is not lawful for him until she marries another husband.

Hazrat Abu Al-Hasan (Mawla Bani Naufal) says that both my wife and I were slaves. I gave her two divorces. Then both of us were freed. I wanted to reconcile with her. I asked Hazrat Ibn Abbas (may Allah be pleased with them) about this, so he said that if you reconcile with her, you will do so with the right of one divorce remaining. Two divorces have passed. The Messenger of Allah (peace and blessings be upon him) also gave the same verdict.

It is narrated similarly through another chain.

Hazrat Abu Salamah and Hazrat Jabir bin Abdullah (may Allah be pleased with them) state that if she is freed during her waiting period (‘iddah), then the husband, if he wishes, may marry her, and he will retain the right to one divorce with her.