Īśāvāsyopaniṣat 03
असुर्या नाम ते लोका अन्धेन तमसाऽवृताः। तान् ते प्रेत्याभिगच्छन्ति ये के चात्महनो जनाः ॥३॥
[असुर्या (asuryā) - Asura-like; नाम (nāma) - named; ते (te) - those; लोकाः (lokāḥ) - worlds; अन्धेन (andhena) - by darkness; तमसाऽवृताः (tamasā'vṛtāḥ) - enveloped in ignorance; तान् (tān) - them; ते (te) - they; प्रेत्याभिगच्छन्ति (pretyābhigacchanti) - attain after death; ये (ye) - who; के च (ke ca) - some; आत्महनो (ātmahano) - killers of the self; जनाः (janāḥ) - people; ]
Those worlds named 'Asura', i.e. demoniacal, are enveloped in the darkness of ignorance. Those killers of the self (i.e. those who do not take authentic honest actions), attain them after death.
Īśā.Bhāshya 03
'Asurya' - having the nature to delight in contrary to good. Also, it is opposite of 'sura', i.e. gods. Thus it means those who turn away from lord Hari.
सुष्ठु रमणविरुद्धत्वात् असुराणां प्राप्यत्वाच्च असुर्याः।
Those who delight in contrary to good are demons. Having such a nature is 'asuryā', i.e. demoniacal.
"न च रमन्त्यहो असदुपासनया आत्महन"
"Indeed, they are not happy. They worship the non existent, promote nihilism, and are killers of the self."
इत्युक्तत्वात्।
- because it is stated thus in the testimonial (Bhagavata Purana).
"महादुःखैकहेतुत्वात् प्राप्यत्वादसुरैस्तथा। असुर्या नाम ते लोका तान्यान्ति विमुखा हरौ॥"
"The demons acquire them as they are the sole cause of the intense suffering. Those worlds are called 'Asurya', i.e. opposed to 'sura' i.e. gods, as those who turn away from lord Hari attain them."
इति वामने।
- thus stated in the Vāmana Purāna.
ये के चेति नियम उक्तः।
By stating 'ye ke', i.e. 'those who', the rule is conveyed (i.e. those opposed to the lord mandatorily attain darkness).
"नियमेन तमो यान्ति सर्वेऽपि विमुखा हरौ।"
"By rule, all, turned away from Hari, attain darkness"
इति च ॥३॥
- there are such testimonials as well.