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.
Yājñavalkya goes to the sun and brings back from there the science of seeing the light within: five spaces, their signs, their stages. It ends by speaking not of himself, but of others.