अनुद्वेगकरं वाक्यं सत्यं प्रियहितं च यत् |
स्वाध्यायाभ्यसनं चैव वाङ्मयं तप उच्यते || 15||
anudvega-karaṁ vākyaṁ satyaṁ priya-hitaṁ cha yat
svādhyāyābhyasanaṁ chaiva vāṅ-mayaṁ tapa uchyate
BG 17.15: Words that do not cause distress, are truthful, inoffensive, and beneficial, as well as the regular recitation of the Vedic scriptures—these are declared as the austerity of speech.