Sahih al-Bukhari, Book 23, Hadith 131 (In-Book) ⓘ

Narrated Ibn `Abbas: The Prophet once passed by two graves and said, "They (the deceased persons in those graves) are being tortured not for a great thing to avoid." And then added, "Yes, (they are being punished for a big sin), for one of them used to go about with calumnies while the other never saved himself from being soiled with his urine." (Ibn `Abbas added): Then he took a green leaf of a date-palm) and split it into two pieces and fixed one piece on each grave and said, "May their punishment be abated till these (two pieces) get dry."

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ مُجَاهِدٍ، عَنْ طَاوُسٍ، قَالَ ابْنُ عَبَّاسٍ ـ رضى الله عنهما ـ مَرَّ النَّبِيُّ صلى الله عليه وسلم عَلَى قَبْرَيْنِ فَقَالَ ‏"‏ إِنَّهُمَا لَيُعَذَّبَانِ، وَمَا يُعَذَّبَانِ مِنْ كَبِيرٍ ـ ثُمَّ قَالَ ـ بَلَى أَمَّا أَحَدُهُمَا فَكَانَ يَسْعَى بِالنَّمِيمَةِ، وَأَمَّا أَحَدُهُمَا فَكَانَ لاَ يَسْتَتِرُ مِنْ بَوْلِهِ ‏"‏‏.‏ قَالَ ثُمَّ أَخَذَ عُودًا رَطْبًا فَكَسَرَهُ بِاثْنَتَيْنِ ثُمَّ غَرَزَ كُلَّ وَاحِدٍ مِنْهُمَا عَلَى قَبْرٍ، ثُمَّ قَالَ ‏"‏ لَعَلَّهُ يُخَفَّفُ عَنْهُمَا مَا لَمْ يَيْبَسَا ‏"‏‏.‏