In chapter 3 of the Kaushitaki Upanishad, the prince Pratardana, son of the famous king Divodasa and seer of a Vedic hymn as I discuss here, dies and goes to Devaloka (heaven), where he meets Indra. Indra offers him a boon, and Pratardana asks Indra to give him whatever boon is most beneficial. So Indra decides to tell him about Indra himself! (This isn't as absurd as it sounds, because Brahman is the soul of the gods and thus truly understanding Indra will allow you to understand Brahman.) In particular, Indra says this about himself:
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.
The Aitareya Brahmana of the Rig Veda says the same thing.
When the gods excluded Indra (saying) 'He hath misused Vishvarupa, Tvastri's son, he hath laid low Vritra, he hath given the Yatis [Sanyasis] to the hyaenas, he hath killed the Arurmaghas, he hath contended with Brhaspati', then Indra was deprived of the Soma drinking[.]
My question is, what is the story of Indra delivering the "devotees" or Sanyasis known as the Arunmukhas to the wolves? Presumably that means they were devoured by wolves.
Sayana, the famous commentator on the Vedas says that the Arunmukhas were actually Asuras in the disguise of Sanyasis, and he characterizes them as "those in whose mouths the reading of the Vedas is not". He also says "their skulls were turned into the thorns of the desert which remain to this day".
But does anyone know if this story is described in any Hindu scripture?