It is narrated from Hazrat Shuraid (may Allah be pleased with him) that his mother advised him to free a Muslim slave on her behalf. He asked the Prophet Muhammad (peace and blessings be upon him) about this, saying: "I have a slave woman from the Nubia region of Abyssinia. Can I free her?" The Prophet Muhammad (peace and blessings be upon him) said: "Bring her to me." I brought her and she came. The Prophet Muhammad (peace and blessings be upon him) asked her: "Who is your Lord?" She replied: "Allah." The Prophet Muhammad (peace and blessings be upon him) asked: "Who am I?" She replied: "You are the Messenger of Allah." The Prophet Muhammad (peace and blessings be upon him) said: "Free her, for she is a Muslim."
Hadith Referenceمسند احمد / تتمہ مُسْنَدِ الْكُوفِيِّينَ / 19455