MUṆḌAKA UPANISHAD · 1.2.2

यदा लेलायते ह्यर्चिः समिद्धे हव्यवाहने ।
तदाऽऽज्यभागावन्तरेणाऽऽहुतीः प्रतिपादयेच्छ्रद्धया हुतम् ॥ २॥

yadā lelāyate hyarciḥ samiddhe havyavāhane ।
tadā’’jyabhāgāvantareṇā’’hutīḥ pratipādayecchraddhayā hutam ॥ 2॥

When the fire of the sacrifice is kindled and the flame sways and quivers, then between the double pourings of butter cast therein with faith thy offerings.