Ishavasyopanishad - 5

Mantra 3

असूर्या नाम ते लोका अन्धेन तमसावृता:

तांस्ते प्रेत्याभिगच्छन्ति ये के चात्महनो जन: |

Devilish are the worlds covered over by dense darkness, which are reached by those who have killed their Self.

The regions experienced by the destroyers of the Self, i.e., those who are ignorant of the Self, are devilish or godless, because they are destitute of purity and light, devoid of sattva-guna, cut off from the knowledge of Truth. They are devilish because experiences, there are extremely painful and antagonistic to the Divine Presence. People who reject the Divine Self and love the undivine matter, which is subjectively called the body and objectively the world, have such experiences as are characterised by extreme repentance for having committed the evil of not knowing the Self. The asuras or the devils are those who have deserted the One Immutable Being.

In this sense all individuals are asuras in different degrees, because they experience the material sheaths or the bodies. These realms of these unfortunate beings are enveloped by dense darkness in the night of the Self. A desire that is a desertion of Truth takes a form later which gives very unpleasant experiences to the desirer, because his experience is opposite to Absolute-Experience. Such people grope in spiritual darkness or blindness, which is the mother of sorrow. Into such dark regions do these who are untrue to their Self enter. They get bad births. A bad birth is a condition of life where craving is the ruler, where mistake is the governing law, where confusion and delusion are the factors controlling life, where evil is perpetrated and intense sorrow is experienced. This is the fruit of not knowing Truth and catching untruth, the result of the wandering of the jiva in the waterless desert of samsara, the effect of eating the forbidden fruit, the fruit of mental and sensuous contacts which sow the seed of the torture of transmigration.