Sahih Bukhari | Volume 1 | Hadith Number 448
Narrated by Abu Huraira
A black man or a black woman used to sweep the mosque and he or she died. The Prophet 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."