Musnad Abu Ya'la al-Mawsili 160:34

And with his chain of narration from Abu Hurairah, that a man used to pick up harmful things from the mosque, then he died. The Prophet, may Allah bless him and grant him peace, missed him and said, "What happened to so-and-so?" They said, "He died." He said, "Why did you not inform me about him?" It was as if they had considered his matter insignificant. So he said to his companions, "Go and show me his grave." He went and prayed over him, then said, "Indeed, these graves are filled with darkness for their inhabitants, and indeed Allah illuminates them for them through my prayer."