Narrated Abu Hurairah:

A man brought the Prophet ﷺ a black slave girl. He said: Messenger of Allah, emancipation of believing slave is due to me. He asked her: Where is Allah ? She pointed to the heaven with her finger. He then asked her: Who am I ? She pointed to the Prophet ﷺ and to the heaven, that is to say: You are the Messenger of Allah. He then said: Set her free, she is a believer.

حَدَّثَنَا إِبْرَاهِيمُ بْنُ يَعْقُوبَ الْجُوزَجَانِيُّ، حَدَّثَنَا يَزِيدُ بْنُ هَارُونَ، قَالَ أَخْبَرَنِي الْمَسْعُودِيُّ، عَنْ عَوْنِ بْنِ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، عَنْ أَبِي هُرَيْرَةَ، : أَنَّ رَجُلاً، أَتَى النَّبِيَّ ﷺ بِجَارِيَةٍ سَوْدَاءَ فَقَالَ : يَا رَسُولَ اللَّهِ إِنَّ عَلَىَّ رَقَبَةً مُؤْمِنَةً . فَقَالَ لَهَا : " أَيْنَ اللَّهُ " . فَأَشَارَتْ إِلَى السَّمَاءِ بِأُصْبُعِهَا . فَقَالَ لَهَا : " فَمَنْ أَنَا " . فَأَشَارَتْ إِلَى النَّبِيِّ ﷺ وَإِلَى السَّمَاءِ، يَعْنِي أَنْتَ رَسُولُ اللَّهِ . فَقَالَ : " أَعْتِقْهَا فَإِنَّهَا مُؤْمِنَةٌ " .