Muṇḍaka Upaniṣad 1.1.5

1.1.5

tatrāparā ṛgvedo yajurvedaḥ sāmavedo 'tharvavedaḥ śikṣā kalpo
vyākaraṇaṃ niruktaṃ chando jyotiṣam iti.
atha parā yayā tad akṣaram
adhigamyate.

5. Of these, the lower is the Rig-Veda, the Yajur-Veda, the Sāma-Veda, the Atharva-Veda, Pronunciation (śikṣā), Ritual (kalpa), Grammar (vyākaraṇa), Definition (nirukta), Metrics (chandas), and Astrology (jyotiṣa).

Now, the higher is that whereby that Imperishable (akṣara) is apprehended.