Muṇḍaka Upaniṣad 1.1.1

1.1.1

brahmā devānāṃ prathamaḥ sambabhūva viśvasya kartā bhuvanasya goptā.
sa brahmavidyāṃ sarvavidyāpratiṣṭhām atharvāya jyeṣṭhaputrāya prāha.

1. Brahmā arose as the first of the gods—
The maker of all, the protector of the world.
He told the knowledge of Brahma (brahma-vidyā), the foundation of all knowledge,
To Atharva[n], his eldest son.