Mundaka Upanishad 1.1

Brahmâ was the first of the Devas, the maker of the universe, the preserver of the world. He told the knowledge of Brahman, the foundation of all knowledge, to his eldest son Atharva.

Whatever Brahmâ told Atharvan, that knowledge of Brahman Atharvan formerly told to Angir; he told it to Satyavâha Bhâradvâga, and Bhâradvâga told it in succession to Angiras.

Saunaka, the great householder, approached Angiras respectfully and asked: "Sir, what is that through which, if it is known, everything else becomes known?"

He said to him: "Two kinds of knowledge must be known, this is what all who know Brahman tell us, the higher and the lower knowledge."

"The lower knowledge is the Rig-veda, Yagur-veda, Sâma-veda, Atharva-veda, Sikshâ (phonetics), Kalpa (ceremonial), Vyâkarana (grammar), Nirukta (etymology), Khandas (metre), Gyotisha (astronomy); but the higher knowledge is that by which the Indestructible (Brahman) is apprehended."

That which cannot be seen, nor seized, which has no family and no caste, no eyes nor ears, no hands nor feet, the eternal, the omnipresent (all-pervading), infinitesimal, that which is imperishable, that it is which the wise regard as the source of all beings."

As the spider sends forth and draws in its thread, as plants grow on the earth, as from every man hairs spring forth on the head and the body, thus does everything arise here from the Indestructible.

The Brahman swells by means of brooding (penance); hence is produced matter (food); from matter breath, mind, the true, the worlds (seven), and from the works (performed by men in the worlds), the immortal (the eternal effects, rewards, and punishments of works).

From him who perceives all and who knows all, whose brooding (penance) consists of knowledge, from him (the highest Brahman) is born that Brahman, name, form, and matter (food)."