Bhagavad Gita 9.16
I am the oblation, the sacrifice, and the worship; I am the fuel and the chant; I am the butter offered to the fire; I am the fire itself, and I am the act of offering.
अहं क्रतुरहं यज्ञः स्वधाऽहमहमौषधम्।
मंत्रोऽहमहमेवाज्यमहमग्निरहं हुतम्॥ahaṃ kraturahaṃ yajñaḥ svadhā'hamahamauṣadham|
maṃtro'hamahamevājyamahamagnirahaṃ hutam||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).