Bhagwad Gita
Chapter 17, Verse 24
तस्मादोमित्युदाहृत्य यज्ञदानतपःक्रियाः।प्रवर्तन्ते विधानोक्ताः सततं ब्रह्मवादिनाम्।।17.24।।
Thus the transcendentalists undertake sacrifices, charities, and penances, beginning always with om, to attain the Supreme.