Bhagwad Gita
Chapter 6, Verse 35
श्री भगवानुवाच
असंशयं महाबाहो मनो दुर्निग्रहं चलं।
अभ्यासेन तु कौन्तेय वैराग्येण च गृह्यते।।6.35।।
The Blessed Lord said: O mighty-armed son of Kunti, it is undoubtedly very difficult to curb the restless mind, but it is possible by constant practice and by detachment.