Bhagavad Gita 17.16

मनःप्रसादः सौम्यत्वं मौनमात्मविनिग्रहः।भावसंशुद्धिरित्येतत्तपो मानसमुच्यते ॥१७.१६॥

manaḥprasādaḥ saumyatvaṃ maunamātmavinigrahaḥbhāvasaṃśuddhirityetattapo mānasamucyate

Serenity of mind, good-heartedness, self-control, and purity of nature—this is called mental austerity.

गीता