Chāndogya Upaniṣad 7.5.3

7.5.3

sa yaś cittaṃ brahmety upāste \
cittān vai sa lokān dhruvān dhruvaḥ pratiṣṭhitān pratiṣṭhito 'vyathamānān avyathamāno 'bhisidhyati \
yāvac cittasya gataṃ tatrāsya yathākāmacāro bhavati yaś cittaṃ brahmety upāste \
asti bhagavaś cittād bhūya iti \
cittād vāva bhūyo 'stīti \
tan me bhagavān bravītv iti \\705.3\

3. He who reverences Thought as Brahma—he, verily, attains the Thought-worlds; himself being enduring, the enduring worlds; himself being established, the established worlds; himself being unwavering, the unwavering worlds. As far as Thought goes, so far he has unlimited freedom, he who reverences Thought as Brahma.’ ‘Is there, Sir, more than Thought?’ ‘There is, assuredly, more than Thought.’ ‘Do you, Sir, tell me it.’