satyaṁ priya-hitaṁ ca yat
vāṅ-mayaṁ tapa ucyate
anudvega-karam — not agitating; vākyam — words; satyam — truthful; priya — dear; hitam — beneficial; ca — also; yat — which; svādhyāya — of Vedic study; abhyasanam — practice; ca — also; eva — certainly; vāk-mayam — of the voice; tapaḥ — austerity; ucyate — is said to be.
Austerity of speech consists in speaking words that are truthful, pleasing, beneficial, and not agitating to others, and also in regularly reciting Vedic literature.
. . .
अनुद्वेगकरं वाक्यं सत्यं प्रियहितं च यत् ।
स्वाध्यायाभ्यसनं चैव वाङ्मयं तप उच्यते ॥ १५ ॥