ŚVETĀŚVATARA UPANISHAD · 3.7

ततः परं ब्रह्म परं बृहन्तं यथानिकायं सर्वभूतेषु गूढं ।
विश्वस्यैकं परिवेष्टितारम् ईशं तं ज्ञात्वामृता भवन्ति ॥

tataḥ paraṃ brahma paraṃ bṛhantaṃ yathānikāyaṃ sarvabhūteṣu gūḍhaṃ ।
viśvasyaikaṃ pariveṣṭitāram īśaṃ taṃ jñātvāmṛtā bhavanti ॥

Those who know beyond this the High Brahman, the vast, hidden in the bodies of all creatures, and alone enveloping everything, as the Lord, they become immortal.