Awn bin Abdullah (may Allah have mercy on him) narrated through his father from his grandfather, Sayyiduna Utbah bin Mas'ud (may Allah be pleased with him): A woman came to the Messenger of Allah (peace and blessings be upon him) with a black slave-girl and said: O Messenger of Allah, I am obliged to free a believing slave; will this one suffice? The Messenger of Allah (peace and blessings be upon him) asked (the slave-girl): "Who is your Lord?" She said: Allah is my Lord. He (peace and blessings be upon him) asked: "What is your religion?" She said: Islam. He (peace and blessings be upon him) asked: "Who am I?" She said: You are the Messenger of Allah. He (peace and blessings be upon him) asked: "Do you testify that I am the Messenger of Allah?" She said: Yes, I testify that you are the Messenger of Allah. He (peace and blessings be upon him) asked: "And do you pray the five prayers?" She said: Yes. He (peace and blessings be upon him) asked: "And do you fast Ramadan?" She said: Yes. He (peace and blessings be upon him) asked: "And do you affirm what has come from Allah?" She said: Yes. Then he (peace and blessings be upon him) patted her on the back and said: "Free her, for she has sufficed on your behalf."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14410