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]