Old Testament, just a couple verses out of many:
Isaiah 33:11-14
Ye shall conceive chaff, ye shall bring forth stubble: your breath, as fire, shall devour you. And the people shall be as the burnings of lime: as thorns cut up shall they be burned in the fire. Hear, ye that are far off, what I have done; and, ye that are near, acknowledge my might. The sinners in Zion are afraid; fearfulness hath surprised the hypocrites. Who among us shall dwell with the devouring fire? who among us shall dwell with everlasting burnings?
Daniel 12:2
And many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt.
There are numerous verses in the OT which speak of the destruction of the wicked and the OT Jews understood this to be everlasting. Now, whether one believes in literal flame or not, the truth is that it is not good. Again, one must accept the whole council of God, not just bits and pieces. As I have said, I believe God is just and he will judge fairly, equally, and if a person is wicked, they will be punished. I would not believe in a God who would let someone murder, rape, steal, lie, blasheme, etc. and not judge them rightly. Either one is wicked or one is righteous, and according to the Bible we are ALL sinners and need a Saviour. So, it still comes down to paying for our sins ourselves or accepting the free gift of salvation because Jesus paid for our sins already.