Ibn ‘Abbas reported the Prophet (ﷺ) as saying, “When a man’s slave-woman bears him a child she becomes free at his death.”* Darimi transmitted it. * The text has 'au durbur in minhu au ba'dahu’ indicating a doubt on the part of a transmitter as to which words were used. Both expressions amount to the same thing so it seems sufficient to give "at his death" in the translation above.