Bhagavad Gita 18.33

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

धृत्या यया धारयते मनःप्राणेन्द्रियक्रियाः।योगेनाव्यभिचारिण्या धृतिः सा पार्थ सात्त्विकी॥

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

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