Bhagavad Gita 6.12
Seated thus, with his mind concentrated, his functions controlled, and his senses governed, let him practice meditation for the purification of his lower nature.
तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः।
उपविश्यासने युञ्ज्याद्योगमात्मविशुद्धये॥tatraikāgraṃ manaḥ kṛtvā yatacittendriyakriyaḥ|
upaviśyāsane yuñjyādyogamātmaviśuddhaye||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).