The Upaniṣads — the philosophical core of the Vedic tradition, revealing the nature of Brahman, the Ātman, knowledge, action and liberation. The ten principal Upaniṣads together with select minor Vaiṣṇava Upaniṣads.
A conversation about what happens after death and who returns and who does not; then a teaching on breath as the chief thing in a person, and on how the gods and senses are held by it. Indra himself teaches Pratardana and speaks of himself in the first person.