From Imām Mālik’s, al-Muwatta:

Description of Jahannum (Hell fire)

[1] Mālik related to me from Abū Zinad from al-A’raj from Abū Hurayrah rađiyAllāhu ánhu that the beloved Messenger of Allah śallAllāhu álayhi wa sallam said,

“The fire of the children of Adam which they kindle is a seventieth part of the fire of Jahannum.” They said, “O Messenger of Allah śallAllāhu álayhi wa sallam, this fire is certainly enough.” He śallAllāhu álayhi wa sallam said, “That fire is sixty-nine times greater.” [Bukhârī 3092 and Muslim]

[2] Mālik related to me from his paternal uncle, Abū Suhayl ibn Mālik, from his father that Abū Hurayrah rađiyAllāhu ánhu said,

Do you think that it is red like this fire of yours? It is blacker than tar.

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]