Musnad Abu Ya'la al-Mawsili 109:67

Qasim ibn Abi Shaybah narrated to us, Abu Dawud al-Tayalisi narrated to us, from Abu al-'Awwam, from Abu al-Zubayr, from Jabir: That the Prophet (peace and blessings of Allah be upon him) passed by two graves and said: "Indeed, they are being punished, and they are not being punished for a major matter. As for one of them, he used to not protect himself from his urine. And as for the other, he used to backbite people."