Bhagavad Gita Chapter 17, Verse 16

मनःप्रसादः सौम्यत्वं मौनमात्मविनिग्रहः | भावसंशुद्धिरित्येतत्तपो मानसमुच्यते ||

manaḥ-prasādaḥ saumyatvaṁ maunam ātma-vinigrahaḥ bhāva-saṁśuddhir ity etat tapo mānasam ucyate

Serenity of mind, gentleness, silence, self-control, and purity of being—this is called mental austerity.

Krishna describes mental austerity—austerity of mind. 'Manaḥ-prasādaḥ saumyatvaṁ maunam ātma-vinigrahaḥ bhāva-saṁśuddhiḥ'—serenity of mind (manaḥ-prasādaḥ), gentleness (saumyatvam), silence (maunam), self-control (ātma-vinigrahaḥ), and purity of being (bhāva-saṁśuddhiḥ). 'Tapo mānasam ucyate'—this is called (ucyate) mental austerity (mānasam tapas). Mental austerity involves cultivating serenity, gentleness, silence, self-control, and purity of intention. This is discipline of mind—developing inner peace and clarity rather than agitation and confusion. Understanding this helps you recognize and practice mental austerity.