Bhagavad Gita Chapter 18, Verse 33
धृत्या यया धारयते मनःप्राणेन्द्रियक्रियाः | योगेनाव्यभिचारिण्या धृतिः सा पार्थ सात्त्विकी ||
dhṛtyā yayā dhārayate manaḥ-prāṇendriya-kriyāḥ yogenāvyabhicāriṇyā dhṛtiḥ sā pārtha sāttvikī
O Arjuna, that firmness which, through unwavering yoga, holds the activities of mind, life force, and senses, is sattvic.
Krishna explains sattvic firmness. 'Dhṛtyā yayā dhārayate manaḥ-prāṇendriya-kriyāḥ yogenāvyabhicāriṇyā'—that firmness (yayā dhṛtiḥ) which, through unwavering yoga (yogena avyabhicāriṇyā), holds (dhārayate) the activities (kriyāḥ) of mind (manaḥ), life force (prāṇa), and senses (indriya). 'Dhṛtiḥ sā pārtha sāttvikī'—that firmness (sā dhṛtiḥ) is sattvic (sāttvikī), O Arjuna (pārtha). This is sattvic firmness: steady, unwavering, holding the mind, senses, and life force through yoga. This is the highest kind of firmness: balanced, steady, unwavering in practice. You maintain control over your mind, senses, and life force with unwavering commitment to yoga. This is the path: steady firmness through unwavering yoga practice, maintaining control and balance.