Patañjali's Yogasūtra I.35

Yogasūtra I.35 - viṣayavatī vā pravṛttiḥ-utpannā manasaḥ sthiti-nibandhinī

The role of the senses, such as hearing, feeling, vision, smell and taste, in providing information to the mind is significant. These senses are the doors of perception and we often become their slaves. But, can we not examine what is even more powerful in us than our senses? Can we not make them sharper and at our disposal?

By regular inquiry into the role of the senses we can reduce mental distortions.