Bulugh al-Maram 555
Abu Hurairah (RAA) narrated regarding the story of the black woman who used to clean the mosque. The Messenger of Allah asked about her, and he was told that she had died. He said to them, “Why didn’t you inform me of her death?" It seems that they regarded her as an insignificant person. The Messenger of Allah (ﷺ) said:
“Show me her grave." They showed him her grave and he offered the funeral prayer for her.’ Agreed upon. Muslim added in his narration, ‘Verily, those graves are full of darkness for those buried in them. Allah, the Almighty, will illuminate them for their dwellers by my prayer over them"
وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- ‏-فِي قِصَّةِ اَلْمَرْأَةِ اَلَّتِي كَانَتْ تَقُمُّ اَلْمَسْجِدَ‏- قَالَ: { فَسَأَلَ عَنْهَا اَلنَّبِيُّ ‏- صلى الله عليه وسلم ‏- ] فَقَالُوا: مَاتَتْ, فَقَالَ: "أَفَلَا كُنْتُمْ آذَنْتُمُونِي"? فَكَأَنَّهُمْ صَغَّرُوا أَمْرَهَا]  1‏ فَقَالَ: "دُلُّونِي عَلَى قَبْرِهَا", فَدَلُّوهُ, فَصَلَّى عَلَيْهَا }  مُتَّفَقٌ عَلَيْهِ  2‏ .‏ 
وَزَادَ مُسْلِمٌ, ثُمَّ قَالَ: { إِنَّ هَذِهِ اَلْقُبُورَ مَمْلُوءَةٌ ظُلْمَةً عَلَى أَهْلِهَا, وَإِنَّ اَللَّهَ يُنَوِّرُهَا لَهُمْ بِصَلَاتِي عَلَيْهِمْ }‏1 ‏- هذه الزيادة غير موجودة بالأصلين، ولكنها في النسخ المطبوعة وأيضا في "الشرح"، وهي أيضا من الحديث ولذلك أبقيتها.‏‏2 ‏- صحيح.‏ رواه البخاري (458)‏، ومسلم (956)‏.‏