नािवरतो दुश्चरितान्नाशान्तो नासमािहतः ।
नाशान्तमानसो वापि प्रज्ञानेनैनाप्नुयात् ॥
nāvirato duścaritān nāśānto nāsamāhitaḥ |
nāśānta-mānaso vāpi prajñānenainam āpnuyāt ||
(Kaṭha Upaniṣad: 1.2.24; cited in the Govinda-bhāṣya on Vedānta-sūtra: 3.3.54; Gītā-bhūṣaṇa-ṭīkā on Śrīmad Bhagavad-gītā: 9.31)
“Neither one who has not desisted from misbehavior, nor one who is devoid of peace [i.e., devoid of control of the senses], nor one who is not steadfast [alt., concentrated], nor one whose mind is devoid of peace, can attain this [i.e., the Ātmā] through knowledge.”