Bg 6.26

yato yato niścalati
manaś cañcalam asthiram
tatas tato niyamyaitad
ātmany eva vaśaṁ nayet
Word for word: 
yataḥ yataḥ — wherever; niścalati — becomes verily agitated; manaḥ — the mind; cañcalam — flickering; asthiram — unsteady; tataḥ tataḥ — from there; niyamya — regulating; etat — this; ātmani — in the Self; eva — certainly; vaśam — control; nayet — must bring under.
Translation: 
From wherever the mind wanders due to its flickering and unsteady nature, one must certainly withdraw it and bring it back under the control of the Self.
Purport: 

The nature of the mind is flickering and unsteady. But a self-realized yogī has to control the mind; the mind should not control him. One who controls the mind (and therefore the senses as well) is called gosvāmī, or svāmī, and one who is controlled by the mind is called go-dāsa, or the servant of the senses. A gosvāmī knows the standard of sense happiness. In transcendental sense happiness, the senses are engaged in the service of Hṛṣīkeśa, or the supreme owner of the senses – Kṛṣṇa. Serving Kṛṣṇa with purified senses is called Kṛṣṇa consciousness. That is the way of bringing the senses under full control. What is more, that is the highest perfection of yoga practice.