Bahr bin Marrar narrated that his grandfather Abu Bakrah said:
"The Messenger of Allah passed by two graves, and he said: 'They are being punished but they are not being punished for anything major. One of them is being punished because of urine, and the other is being punished because of backbiting.'"
English reference: Vol. 1, Book 1, Hadith 349
Arabic reference: Book 1, Hadith 376