Awn bin Abdullah bin Utbah narrates from his father, through his grandfather (may Allah be pleased with him), that a woman came to the Prophet (peace and blessings be upon him) with a black slave girl and said: O Messenger of Allah (peace and blessings be upon him)! I owe the freeing of a believing neck (slave); will this one suffice on my behalf? The Messenger of Allah (peace and blessings be upon him) asked her: "Who is your Lord?" She said: My Lord is Allah. He (peace and blessings be upon him) asked: "What is your religion?" She said: Islam. He (peace and blessings be upon him) said: "Who am I?" She said: You are the Messenger of Allah. He (peace and blessings be upon him) said: "Do you pray the five prayers, and do you affirm what I have brought from Allah?" She said: Yes. He (peace and blessings be upon him) struck her on the back and said: "Free her."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الظهار / 15269