On it being forbidden to sit on graves

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

347. Chapter: On it being forbidden to sit on graves

1766. Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, 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]