Musnad Ahmad 1979

It was narrated that Ibn "Abbas said: The Messenger of Allah (ﷺ) passed by two graves, and he said: “They are being punished, but they are not being punished for anything that was difficult to avoid. One of them did not protect himself from urine - Wakee’ said: from his urine - and the other used to walk around spreading malicious gossip." He called for a palm branch, split it in two, then planted one piece on each grave, Then he said: “Perhaps it will be reduced for them so long as this does not dry out."