Bhagavad Gita 6.34 Chapter 6, Verse 34

चञ्चलं हि मनः कृष्ण प्रमाथि बलवद्दृढम् ।
तस्याहं निग्रहं मन्ये वायोरिव सुदुष्करम् ॥६.३४॥

cañcalaṃ hi manaḥ kṛṣṇa pramāthi balavaddṛḍham
tasyāhaṃ nigrahaṃ manye vāyoriva suduṣkaram

Meaning

For the mind, O Krishna, is restless, turbulent, strong and obstinate. I think controlling it is as hard as controlling the wind.

Newly written by Bhajan Dhun — scholarly review in progress.

Reference: Bhagavad Gita 6.34 (Chapter 6, The Yoga of Meditation (Atma Samyama Yoga), Verse 34)