Ubaydullah bin Abdullah bin Utbah (may Allah have mercy on him) said: A man from the Ansar came to the Prophet (peace and blessings be upon him) with his black slave girl and said: O Messenger of Allah! I owe the freeing of a believing slave; shall I free her? If you consider her a believer, I will free her. He (peace and blessings be upon him) asked: "Do you bear witness that there is no god but Allah?" She said: Yes. He (peace and blessings be upon him) asked: "Do you bear witness that Muhammad (peace and blessings be upon him) is the Messenger of Allah?" She said: Yes. He (peace and blessings be upon him) asked: "Do you believe in being raised after death?" She said: Yes. He (peace and blessings be upon him) said: "Free her."
This is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19986