Greatest type of punishment
Shaikh Uthaymeen, may Allaah have mercy on him, said,
“Many people think that being punished [for one’s sins] is only in those things that are external, like the body, wealth and children, but the reality is that the punishment of the sickness of the heart and its corruption is more severe and greater than the punishment through those things.”
Source: Ahkaam minal-Qur’aanil-Karim, vol. 1, p. 87.