Māṇdūkya Upaniṣad 1.1.5

`The lower knowledge is the Rig-veda, Yagurveda, Sama-veda, Atharva-veda, Siksha (phonetics), Kalpa (ceremonial), Vyakarana (grammar), Nirukta but the higher knowledge is that by which the Indestructible (Brahman) is apprehended.'