مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 338
Purification
How to act when relieving oneself - Section 1
وَعَنِ ابْنِ عَبَّاسٍ قَالَ مَرَّ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِقَبْرَيْنِ فَقَالَ إِنَّهُمَا لَيُعَذَّبَانِ وَمَا يُعَذَّبَانِ فِي كَبِيرٍ أَمَّا أَحدهمَا فَكَانَ لَا يَسْتَتِرُ مِنَ الْبَوْلِ - وَفِي رِوَايَةٍ لمُسلم: لَا يستنزه مِنَ الْبَوْلِ - وَأَمَّا الْآخَرُ فَكَانَ يَمْشِي بِالنَّمِيمَةِ ثمَّ أَخذ جَرِيدَة رطبَة فَشَقهَا نِصْفَيْنِ ثُمَّ غَرَزَ فِي كُلِّ قَبْرٍ وَاحِدَةً قَالُوا يَا رَسُول الله لم صنعت هَذَا قَالَ لَعَلَّه يُخَفف عَنْهُمَا مَا لم ييبسا
Ibn ‘Abbas told that the Prophet (ﷺ) came upon two graves and said, "Their occupants are being punished, but not for a great sin. One of them did not keep himself from being defiled by urine. (A version by Muslim has "did not keep himself undefiled by urine”.) The other went about spreading slander.” He then took a fresh palm branch, split it in two parts, and planted one on each grave. On being asked why he did this, he said, "Perhaps their punishment may be mitigated as long as they remain fresh.” (Bukhari and Muslim.)
Mishkat al-Masabih, 338مُتَّفَقٌ عَلَيْهِ (الألباني)