Kaṭha Upaniṣad 2.12

2.12

taṃ durdarśaṃ gūḍham anupraviṣṭaṃ guhāhitaṃ gahvareṣṭhaṃ purāṇam /
adhyātmayogādhigamena devaṃ matvā dhīro harṣaśokau jahāti //

12. Him who is hard to see, entered into the hidden,
Set in the secret place [of the heart], dwelling in the depth, primeval—
By considering him as God, through the Yoga-study of what pertains to self,
The wise man leaves joy and sorrow behind.