Sankhaya Yog-Bhagavad Gita Chapter 2 [Contents of the Gita Summarized]
Krishna Said > Shaloka: 68
Therefore, O mighty-armed, one whose senses are restrained from their objects is certainly of steady intelligence.
As enemies are curbed by superior force, similarly, the senses, can be curbed not by any human endeavor, but only by keeping them engaged in the service of the Lord. One who has understood this–that only by Krsna consciousness is one really established in intelligence and that one should practice this art under the guidance of a bona fide spiritual master–is called sadhaka, or a suitable candidate for liberation.