Śvetāśvatara Upaniṣad · 5..4

तस्मादग्निः समिधो यस्य सूर्यः सोमात् परिज्यायते दक्षिणाग्निर्यस्य तद्धि वेदा अधिस्वर्यं यज्ञस्य तं वै तं वेदा अधिस्वर्यं यज्ञस्य तं वै तं वेदा अधिस्वर्यं यज्ञस्य

tasmādagniḥ samidho yasya sūryaḥ somāt parijyāyate dakṣiṇāgnir yasya taddhi vedā adhisvaryam yajñasya taṃ vai taṃ vedā adhisvaryam yajñasya taṃ vai taṃ vedā adhisvaryam yajñasya

Therefore, from the fire of firewood arises the sun, from the moon the southern fire. From him are the Vedas, the supremacy of sacrifice —truly, truly, from him are the Vedas, the supremacy of sacrifice.

A sacrificial cosmogony: from earthly agni (fire) arises celestial sūrya (sun); from soma (moon) arises the dakṣiṇāgni (southern fire, used in rituals). From him (tasmat) come the Vedas and the adhisvaryam (supremacy) of yajña (sacrifice). In our yoga practice, this reminds us that all ritual is manifestation of ultimate Reality. The triple affirmation —“truly, truly”— is emphatic: the Vedas are not mere texts but emanations of Reality itself. Sacrifice is both external ritual and internal offering of ego.