Mandukya Karika, verse 3.40


मनसो निग्रहायत्तमभयं सर्वयोगिना(णा)म् ।
दुःखक्षयः प्रबोधश्चाप्यक्षया शान्तिरेव च ॥ ४० ॥

manaso nigrahāyattamabhayaṃ sarvayoginā(ṇā)m |
duḥkhakṣayaḥ prabodhaścāpyakṣayā śāntireva ca || 40 ||

40. The Yogis (who do not follow the method of Jñāna-Yoga as described in the Kārikā) depend on the control of their mind for fearlessness, destruction of misery, the knowledge of self and eternal peace.

Shankara Bhashya (commentary)

Those1 who regard mind and the sense-organs, when seen apart from their identity with the very nature of Brahman, as mere imagination,—like that of the snake when seen apart from its identity with the rope—and who thus deny the sole reality of the mind and the sense-organs (independent of Brahman), i.e., those who look upon themselves as of the very nature of Brahman, spontaneously enjoy, as quite natural to them, fearlessness and eternal peace known as Freedom, (perfect knowledge) for which they (the Jñānis) do not depend upon any mechanical effort (such as the control of the mind, etc.). We have already stated that no duty (effort), whatsoever, exist for the Jñāni. But those other Yogis who are also traversing the path (leading to Truth), but who possess inferior2 or middling understanding and who3 look upon the mind as separate from but related to Ātman, and who4 are ignorant of the knowledge regarding the reality of Ātman—the Yogis belonging to this class can experience fearlessness as a result of the discipline of the mind. To them5 the destruction of misery is also dependent upon mental control. The ignorant can never experience the cessation of misery, if the mind, (considered) related to Ātman, becomes active. Besides, their knowledge of self is dependent on their control of the mind. And similarly, eternal peace, known as Mokṣa (or liberation), in their case, depends upon the mental discipline.