Adhyāya 17 • Shloka 24

तस्मादोमित्युदाहृत्य यज्ञदानतपःक्रियाः | प्रवर्तन्ते विधानोक्ताः सततं ब्रह्मवादिनाम् || २४ ||

tasmād om ity udāhṛtya yajña-dāna-tapaḥ-kriyāḥ | pravartante vidhānoktāḥ satataṁ brahma-vādinām || 24 ||

"Therefore, transcendentalists undertaking performances of sacrifice, charity and penance in accordance with scriptural regulations begin always with om, to attain the Supreme."