6:34  

चञ्चलं हि मनः कृष्ण प्रमाथि बलवद्‌दृढम् ।
तस्याहं निग्रहं मन्ये वायोरिव सुदुष्करम् ॥६- ३४॥

chaJNchalaM hi manaH kRRiShNa pramaathi balawad‌dRRiDham ।

tasyaahaM nigrahaM manye waayoriwa suduShkaram ॥६- ३४॥

Source: Automatic ITRANS Transliteration

So restive the mind, Krishna, churning, strong, stubborn!
I consider its subjugation as difficult as [that of] wind.

Source: Milind S. Pandit

Because the mind, indeed, is very unsteady, turbulent, powerful, and obstinate, O Krishna. I think restraining the mind is as difficult as restraining the wind.

Source: The Bhagavad-Gita: The Sacred Song

For the mind is restless, turbulent, obstinate and very strong, O Krsna, and to subdue it is, it seems to me, more difficult than controlling the wind.

Source: Bhagavad Gita As It Is