Chapter 3 · The Yoga of Action · Krishna said
Bhagavad Gita 3.15 — Brahman in yajna
कर्म ब्रह्मोद्भवं विद्धि ब्रह्माक्षरसमुद्भवम्। तस्मात्सर्वगतं ब्रह्म नित्यं यज्ञे प्रतिष्ठितम् ॥
karma brahmodbhavaṃ viddhi brahmākṣarasamudbhavam | tasmātsarvagataṃ brahma nityaṃ yajñe pratiṣṭhitam ||
Meaning
Know that action arises from the Vedas, and the Vedas come from the Imperishable. So the all-pervading Brahman is always present in yajna.