Bhagavad Gita · 18.33

धृत्या यया धारयते मनःप्राणेन्द्रियक्रियाः।योगेनाव्यभिचारिण्या धृतिः सा पार्थ सात्त्विकी॥

dhṛityā yayā dhārayate manaḥ-prāṇendriya-kriyāḥ yogenāvyabhichāriṇyā dhṛitiḥ sā pārtha sāttvikī

O Partha, that unwavering determination by which one controls the activities of the mind, life-breath, and senses through yoga — that determination is sattvic.

— Bhagavad Gita 18.33

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