Three old men once came to Abba Sisoes because they had heard that he was a great man. And the first one said unto him, “Father, how can I escape from the river of fire” And Abba Sisoes answered him never a word.
Then the second old man said unto him, “Father, how can I escape from the gnashing of teeth, and from the worm which never dies?” And Abba Sisoes answered him never a word.
Then the third old man said unto him, “Father, what shall I do? For the remembrance of the outer darkness troubles me.”
And Abba Sisoes answered and said unto them, “I never think on any of these things, but I believe that God is Merciful, and that He will show mercy unto me.” Then the old men went away grieved at the answer which Abba Sisoes had spoken unto them.
Now because he did not wish to send them away sorrowful, he brought them back, and said unto them, “Blessed are you, O my brethren, for I have been jealous of you”, and they said unto him, “In what matter have you been jealous of us?”
And he said, “The first one of you spoke about a river of fire; and the second spoke about the gnashing of teeth and the worm which dies not; and the third spoke about the outer darkness; if remembrances of this kind have dominion over your minds it is impossible for you to commit sin. What can I do who am stubborn of heart? For hardness of heart will not allow me to perceive even that there a punishment for men exists, and because of this I sin every hour.”
And when the old men had heard these words, they made excuses to him, and said, “In very truth according to what we have heard, even so have we seen.”
[Abba Sisoes, Apophthegmata Patrum]