Anas bin Malik reported,

A black man used to clean the mosque. He died and was buried at night. The Prophet ﷺ was told about it, and he said, "Take me to his grave."So they went to his grave, and he said, "These graves are filled with darkness for their occupants, but Allah illuminates them through my prayer over them."He came to the grave and prayed over him.Then a man from the Ansar said, "Messenger of Allah, my brother died and you did not pray over him."The Prophet asked, "Where is his grave?"The man told him, and the Messenger of Allah ﷺ went with the Ansari.

حدثنا سليمان بن داود حدثنا أبو عامر يعني الخزاز عن ثابت

عن أنس

أن أسود كان ينظف المسجد فمات فدفن ليلا وأتى النبي ﷺ فأخبر فقال انطلقوا إلى قبره فانطلقوا إلى قبره فقال إن هذه القبور ممتلئة على أهلها ظلمة وإن الله عز وجل ينورها بصلاتي عليها فأتى القبر فصلى عليه وقال رجل من الأنصار يا رسول الله إن أخي مات ولم تصل عليه قال فأين قبره فأخبره فانطلق رسول الله ﷺ مع الأنصاري