Bhagavad Gita 17.16

Serenity, kindness, silence, self-control, and purity—these are the austerities of the mind.

मनःप्रसादः सौम्यत्वं मौनमात्मविनिग्रहः।भावसंशुद्धिरित्येतत्तपो मानसमुच्यते॥

manaḥprasādaḥ saumyatvaṃ maunamātmavinigrahaḥ|bhāvasaṃśuddhirityetattapo mānasamucyate||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).