From Imām an-Nawawī’s, Riyadh as-Salihīn:
1766. Abū Hurayrah rađiyAllâhu ánhu reported that the beloved Messenger of Allah śallAllāhu álayhi wa sallam said,
It would be better for one of you to sit on a hot coal which burned his clothes and reached his skin than to sit on a grave. [Muslim]