Chapter 17 · verse 24 · gita.yoga.org

Bhagavad Gita 17.24

तस्मादोमित्युदाहृत्य यज्ञदानतपःक्रियाः।प्रवर्तन्ते विधानोक्ताः सततं ब्रह्मवादिनाम्

Therefore, with the utterance of "Om," the acts of sacrifice, gift, and austerity, as enjoined in the scriptures, are always begun by the students of Brahman.