Bhagavad Gita · 6.34

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

chañchalaṁ hi manaḥ kṛṣhṇa pramāthi balavad dṛḍham tasyāhaṁ nigrahaṁ manye vāyor iva su-duṣhkaram

The mind is indeed restless, O Krishna — turbulent, powerful, and obstinate. I think controlling it is as difficult as controlling the wind.

— Bhagavad Gita 6.34

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)