While I was walking with the Messenger of Allah ﷺ, he was holding my hand, and another man was on his left. We came upon two graves in front of us, and the Messenger of Allah ﷺ said, "These two are being punished, and they are not being punished for something major. Yet indeed it is so. Which of you will bring me a palm branch?"We raced off, and I beat him to it and brought the Messenger of Allah ﷺ a palm branch. He broke it in half and placed one piece on this grave and the other piece on that grave, then said, "It will lighten their punishment as long as they remain fresh. They are being punished only for urine and backbiting."
حدثنا أبو سعيد مولى بني هاشم حدثنا الأسود بن شيبان حدثنا بحر بن مرار عن عبد الرحمن بن أبي بكرة قال حدثنا
بينما أنا أماشي رسول الله ﷺ وهو آخذي بيدي ورجل عن يساره فإذا نحن بقبرين أمامنا فقال رسول الله ﷺ إنهما ليعذبان وما يعذبان في كبير وبلى فأيكم يأتيني بجريدة فاستبقنا فسبقته فأتيته بجريدة فكسرها نصفين فألقى على ذا القبر قطعة وعلى ذا القبر قطعة وقال إنه يهون عليهما ما كانتا رطبتين وما يعذبان إلا في البول والغيبة
Its isnad is sahih. Bahr bin Marrar is the son of Abdul-Rahman bin Abu Bakra, and he narrates from his grandfather. He is trustworthy, and his hadith is found in the collection of Abu Dawud. As for Abdul-Rahman bin Abu Bakra, he is one of the trustworthy Tabiin. This hadith has been mentioned many times before. See 17489.