Musannaf Ibn Abi Shayba 13:1103

Abu Bakr narrated to us, he said: Yazid bin Harun narrated to us, from Ash'ath, from al-Sha'bi, who said: I asked him about a slave girl who ran away from one land to another land, and she came to some people and claimed that she was free. A man desired her and married her, and she bore children. Then they learned that she was a slave, and her master came and took her. He said: The master takes his slave girl, and the father ransoms his children according to the value of a slave (ghurra).