Bhagavadgita 2.58-68

When also, like the tortoise its limbs, he can completely withdraw the senses from their objects, then his wisdom becomes steady.

Objects fall away from the abstinent man, leaving the longing behind. But his longing also ceases, who sees the Supreme.

The turbulent senses, O son of Kunti, do violently snatch away the mind of even a wise man, striving after perfection.

The steadfast, having controlled them all, sits focussed on Me as the Supreme. His wisdom is steady, whose senses are under control.

Thinking of objects, attachment to them is formed in a man. From attachment longing, and from longing anger grows.

From anger comes delusion, and from delusion loss of memory. From loss of memory comes the ruin of discrimination, and from the ruin of discrimination he perishes.

But the self-controlled man, moving among objects with senses under restraint, and free from attraction and aversion, attains to tranquillity.

In tranquillity, all sorrow is destroyed. For the intellect of him who is tranquil-minded, is soon established in firmness.

No knowledge (of the Self) has the unsteady. Nor has he meditation. To the unmeditative there is no peace. And how can one without peace have happiness?

For, the mind which follows in the wake of the wandering senses, carries away his discrimination, as a wind (carries away from its course) a boat on the waters.

Therefore, O mighty-armed, his knowledge is steady, whose senses are completely restrained from their objects.