Kauṣītaki Upaniṣad 3.1

3.1

vijānīyānnāsya kena ca karmaṇāloko mīyate na mātṛvadhena na pitṛvadhena na
steyena na bhrūṇahatyayā nāsyapāpaṃ ca na cakṛṣo mukhānnīlaṃ vetīti

Pratardana, forsooth, the son of Divodâsa (king of Kâsî), came by means of fighting and strength to the beloved abode of Indra. Indra said to him 'Pratardana, let me give you a boon to choose.' And Pratardana answered: 'Do you yourself choose that boon for me which you deem most beneficial for a man.' Indra said to him: 'No one who chooses, chooses for another; choose thyself,' Then Pratardana replied: 'Then that boon to choose is no boon for me.'
Then, however, Indra did not swerve from the truth, for Indra is truth. Indra said to him: 'Know me only; that is what I deem most beneficial for man, that he should know me. I slew the three-headed son of Tvashtri; I delivered the Arunmukhas, the devotees, to the wolves (sâlâvrika); breaking many treaties, I killed the people of Prahlâda in heaven, the people of Puloma in the sky, the people of Kâlakañga on earth. And not one hair of me was harmed there. And he who knows me thus, by no deed of his is his life harmed, not by the murder of his mother, not by the murder of his father, not by theft, not by the killing of a Brahman. If he is going to commit a sin, the bloom does not depart from his face.'