Bahr bin Marrar narrated that his grandfather Abu Bakrah said:"The Messenger of Allah passed by two graves, and he said: 'They are being punished but they are not being punished for anything major. One of them is being punished because of urine, and the other is being punished because of backbiting.'"
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا الأَسْوَدُ بْنُ شَيْبَانَ، حَدَّثَنِي بَحْرُ بْنُ مَرَّارٍ، عَنْ جَدِّهِ أَبِي بَكْرَةَ، قَالَ مَرَّ النَّبِيُّ ـ صلى الله عليه وسلم ـ بِقَبْرَيْنِ فَقَالَ " إِنَّهُمَا لَيُعَذَّبَانِ وَمَا يُعَذَّبَانِ فِي كَبِيرٍ أَمَّا أَحَدُهُمَا فَيُعَذَّبُ فِي الْبَوْلِ وَأَمَّا الآخَرُ فَيُعَذَّبُ فِي الْغِيبَةِ " .
IbnMaja
The Book of Purification and its Sunnah • Hadith 349