Here is Revelation 20:10 from The New Greek English Interlinear New Testament, by Robert K. Brown and Philip W. Comfort:
AND THE DEVIL, THE ONE DECEIVING THEM, WAS THROWN INTO THE LAKE OF FIRE AND SULPHUR, WHERE BOTH THE BEAST AND THE FALSE PROPHET {ARE}, AND THEY WILL BE TORMENTED DAY AND NIGHT INTO THE AGES OF THE AGES.
"They will be tormented day and night into the ages of the ages" means they will be suffering forever and forever. This would not be true if one is turned to ashes and annihilated. Please also notice the future tense, "WILL BE TORMENTED DAY AND NIGHT." There is no annihilation of the wicked.
AND THE DEVIL, THE ONE DECEIVING THEM, WAS THROWN INTO THE LAKE OF FIRE AND SULPHUR, WHERE BOTH THE BEAST AND THE FALSE PROPHET {ARE}, AND THEY WILL BE TORMENTED DAY AND NIGHT INTO THE AGES OF THE AGES.
"They will be tormented day and night into the ages of the ages" means they will be suffering forever and forever. This would not be true if one is turned to ashes and annihilated. Please also notice the future tense, "WILL BE TORMENTED DAY AND NIGHT." There is no annihilation of the wicked.