وَحَدَّثَنِي مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ بْنِ مَسْعُودٍ، أَنَّ رَجُلاً، مِنَ الأَنْصَارِ جَاءَ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم بِجَارِيَةٍ لَهُ سَوْدَاءَ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّ عَلَىَّ رَقَبَةً مُؤْمِنَةً فَإِنْ كُنْتَ تَرَاهَا مُؤْمِنَةً أُعْتِقُهَا ‏.‏ فَقَالَ لَهَا رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَتَشْهَدِينَ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ ‏"‏ ‏.‏ قَالَتْ نَعَمْ ‏.‏ قَالَ ‏"‏ أَتَشْهَدِينَ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ قَالَتْ نَعَمْ ‏.‏ قَالَ ‏"‏ أَتُوقِنِينَ بِالْبَعْثِ بَعْدَ الْمَوْتِ ‏"‏ ‏.‏ قَالَتْ نَعَمْ ‏.‏ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَعْتِقْهَا ‏"‏ ‏.‏

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." Translation Not Available

Book Ref: Muwatta Imam Malik Book 38 Hadith 1474
Web Ref:  Muwatta Imam Malik Book 38 Hadith 9