Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) passed by two graves and he (peace and blessings be upon him) said: "These two are being punished, and they are not being punished for some great matter. One of them used to go about carrying tales, and the other did not guard himself from the splashes of urine." Then he (peace and blessings be upon him) took a fresh palm stalk, split it into two parts and planted them on the graves. The people said: Why did you do this? He (peace and blessings be upon him) said: "I hope that their punishment will be lightened until they dry."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4140