Bhagavad Gita 18.33

धृत्या यया धारयते मनःप्राणेन्द्रियक्रियाः।योगेनाव्यभिचारिण्या धृतिः सा पार्थ सात्त्विकी॥

dhṛtyā yayā dhārayate manaḥprāṇendriyakriyāḥ |yogenāvyabhicāriṇyā dhṛtiḥ sā pārtha sāttvikī ||

The unwavering firmness, through which Yoga restrains the functions of the mind, life-force, and senses—that firmness, O Arjuna, is Sattvic (pure).

The conviction and steady concentration with which the mind, the energy, and the senses are controlled—O Arjuna!—are the result of purity.

Our plain-language meaning of this verse is waiting for scholar review.