śraddhātrayavibhāgayoga - Verse śloka 15
śloka 15
anudvegakaraṃ vākyaṃ satyaṃ priyahitaṃ ca yat |
svādhyāyābhyasanaṃ caiva vāṅmayaṃ tapa ucyate ||17-15||
Translation
Speech that does not cause agitation, that is pleasing, beneficial and true, and the study of the Vedas—this is called austerity of speech.