Verse
तस्मादोमित्युदाहृत्य यज्ञदानतपःक्रियाः ।प्रवर्तन्ते विधानोक्ताः सततं ब्रह्मवादिनाम् ॥
Therefore with the pronunciation of OM the acts of sacrifice, giving and askesis as laid down in the rules are always commenced by the knowers of the Brahman.
Gītā 17·24