Malik related to me from Ibn Shihab from Ubaydullah ibn Abdullahibn Utba ibn Masud that one of the Ansar came to the Messenger ofAllah, may Allah bless him and grant him peace, with a black slave-girl of his. He said, "Messenger of Allah, I must set a slave free whois a mumina. If you think that she is mumina, I will free her." TheMessenger of Allah, may Allah bless him and grant him peace,questioned her, "Do you testify that there is no god but Allah?" Shesaid, "Yes." "Do you testify that Muhammad is the Messenger of Allah?"She said, "Yes." "Are you certain about the rising after death?" Shesaid, "Yes." The Messenger of Allah, may Allah bless him and grant himpeace, said, "Free her."
USC-MSA web (English) reference: Book 38, Hadith 9
Arabic reference: Book 38, Hadith 1474