A black man or a black woman used to sweep the mosque and he or she died. The Prophet ﷺ asked about her (or him). He was told that she (or he) had died. He said, "Why did you not inform me? Show me his grave (or her grave)." So he went to her (his) grave and offered her (his) funeral prayer."  

أَنَّ رَجُلاً أَسْوَدَ أَوِ امْرَأَةً سَوْدَاءَ كَانَ يَقُمُّ الْمَسْجِدَ فَمَاتَ فَسَأَلَ النَّبِيُّ ﷺ عَنْهُ فَقَالُوا مَاتَ قَالَ أَفَلاَ كُنْتُمْ آذَنْتُمُونِي بِهِ دُلُّونِي عَلَى قَبْرِهِ أَوْ قَالَ قَبْرِهَا فَأَتَى قَبْرَهُ فَصَلَّى عَلَيْهِ