Mundaka Upanishad Verse 2.2.9
Sanskrit Verse
हिरण्मये परे कोशे विरजं ब्रह्म निष्कलम् ।
तच्छुभ्रं ज्योतिषं ज्योतिस्तद्यदात्मविदु विदुः ॥ ९ ॥
Transliteration
hiraṇmaye pare kośe virajaṃ brahma niṣkalam |
tacchubhraṃ jyotiṣaṃ jyotistadyadātmavido viduḥ || 9 ||
Translation
The stainless indivisible Brahman, the pure, the light of all lights is in the innermost sheath of golden hue. That is what the knowers of the Atman know.

Muni's Play