Musannaf Ibn Abi Shayba 13:3384

Abu Bakr narrated to us, he said: Yahya bin Sa'id narrated to us, he said: 'Ubaydullah bin Rifa'ah al-Ansari informed me, he said: It was said to a man, "It is mentioned that you are buying such-and-such a slave woman," and they named her. The man said, "If I buy her, then she is free." 'Abdullah claimed that he asked Sa'id bin al-Musayyib, and he said, "As for me, I do not consider it to be anything." And as for 'Umar bin 'Abd al-'Aziz, he rejects it.