It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that there was a black man or woman who used to sweep the mosque. He/she passed away. When the Noble Prophet (peace and blessings be upon him) did not see him/her, he (peace and blessings be upon him) asked: What happened to the one who used to clean the mosque? Someone said: He/she has passed away. The Prophet (peace and blessings be upon him) said: Why did you not inform me? The companions said: It happened at night. The Prophet (peace and blessings be upon him) said: Guide me to his/her grave. So the Prophet (peace and blessings be upon him) went to the grave and performed the funeral prayer. The narrator of this hadith, Thabit, while narrating this or another hadith, said that the Prophet (peace and blessings be upon him) said: Indeed, these graves are filled with darkness, and because of my prayer, Allah Almighty has illuminated them.