मनःप्रसादः सौम्यत्वं मौनमात्मविनिग्रहः।
17.16. The serenity of mind, the ietness, the taciturnity, the self-control, the purity of thought-all this is called mental austerity.
17.14-16 Deva - etc. upto manasam ucyate : Honesty : uprightness, i.e., the courage regarding what needs no hiding. Which is true : This is explained by Which is pleasant and beneficial. Pleasant : at the time of [hearing] that speech. And beneficial : something in future. This type of speech, but not merely speaking what actually happened, is called speaking the truth. Purity of thought : Thought denotes intention; its highest purity.
Manahprasaadah saumyatwam maunamaatmavinigrahah; Bhaavasamshuddhirityetat tapo maanasamuchyate.
manaḥ-prasādaḥ—serenity of thought; saumyatvam—gentleness; maunam—silence; ātma-vinigrahaḥ—self-control; bhāva-sanśhuddhiḥ—purity of purpose; iti—thus; etat—these; tapaḥ—austerity; mānasam—of the mind; uchyate—are declared as