Musnad Ahmad 785:13

Muhanna ibn Abd al-Hamid narrated to us, Abdullah said, my father said: His kunya is Abu Shibl, Hammad—meaning Ibn Salamah—narrated to us, from Muhammad ibn Amr, from Abu Salamah, from al-Sharid, that his mother bequeathed that a slave be emancipated on her behalf. He said: "O Messenger of Allah, my mother bequeathed that a believing slave be emancipated on her behalf, and I have a black Nubian slave girl." He said: "Call her." So he brought her, and the Prophet, peace and blessings of Allah be upon him, said to her: "Who is your Lord?" She said: "Allah." He said: "Who am I?" She said: "You are the Messenger of Allah." He said: "Emancipate her, for she is a believer."