Musannaf Ibn Abi Shayba 9:585

Jarir narrated to us, from Mughira, from Hammad, from Ibrahim, who said: If a male slave has a free wife, and the master of the male slave dies, and his wife inherits her share from him, then if she emancipates him on the spot, they remain upon their first marriage. But if she does not emancipate him, she becomes forbidden to him.