CC Madhya 6.133
- upaniṣad-śabde yei mukhya artha haya
- sei artha mukhya,—vyāsa-sūtre saba kaya
upaniṣad—of the Vedas; śabde—by the words; yei—whatever; mukhya—direct; artha—meaning; haya—is; sei—that; artha—meaning; mukhya—chief; vyāsa-sūtre—in the Vedānta-sūtra; saba—all; kaya—describes.
Caitanya Mahāprabhu continued, “The Vedānta-sūtra is the summary of all the Upaniṣads; therefore whatever direct meaning is there in the Upaniṣads is also recorded in the Vedānta-sūtra, or Vyāsa-sūtra.
Śrīla Bhaktisiddhānta Sarasvatī has explained the word upaniṣad in his Anubhāṣya. Please refer to Adi-līlā, Second Chapter, fifth verse, and Ādi-līlā, Seventh Chapter, verses 106 and 108, for his explanation.