Musannaf Ibn Abi Shayba 9:711

Ibn Mahdi and Yazid ibn Harun narrated to us, from Hisham al-Dastawa'i, from Yahya ibn Abi Kathir, from Sawwar al-Kufi, from Abdullah, who said: "The free woman is to be consulted, and the slave woman is to be dismissed [from her marriage/status]."