Sahih Adab al-Mufrad

It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that we were with the Messenger of Allah (peace and blessings of Allah be upon him) when he came to two graves, the occupants of which were being punished. The Messenger of Allah (peace and blessings of Allah be upon him) said: "They are not being punished for something major. And why not? One of them used to backbite people, and the other did not take care to protect himself from urine (splashes)." Then the Messenger of Allah (peace and blessings of Allah be upon him) called for a fresh date-palm branch or two branches, then he broke them and ordered that a branch be planted on each grave. Then the Messenger of Allah (peace and blessings of Allah be upon him) said: "Listen! Their punishment will be lightened as long as these remain fresh," or he said: "until they dry out."