Bhagavad Gita · 6.12

तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः।उपविश्यासने युञ्ज्याद्योगमात्मविशुद्धये॥

tatraikāgraṁ manaḥ kṛtvā yata-chittendriya-kriyaḥ upaviśhyāsane yuñjyād yogam ātma-viśhuddhaye

Sitting on that seat, making the mind one-pointed by controlling the thoughts, senses, and activities, one should practice yoga for the purification of the self.

— Bhagavad Gita 6.12

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)