KRISHNA:

A man is said to be confirmed in spiritual knowledge when he foresaketh every desire which entereth into his heart, and of himself is happy and content in the Self through the Self. His mind is undisturbed in adversity; he is happy and contented in prosperity, and he is a stranger to anxiety, fear and anger. Such a man is called a Muni. When in every condition he receives each event, whether favorable or unfavorable, with an equal mind which neither likes nor dislikes, his wisdom is established, and, having met good or evil, neither rejoiceth at the one, nor is cast down by the other. He is confirmed in spiritual knowledge, when, like a tortoise, he can draw in all his senses and restrain them from their wonted purposes. The hungry man loseth sight of every other object but the gratification of his appetite, and when he is become acquainted with the Supreme, he loseth all taste for objects of whatever kind. The tumultuous senses and organs hurry away by force the heart, even of the wise man who striveth after perfection. Let a man, restraining all these, remain in devotion at rest with me, his true self; for he who hath his senses and organs in control possesses spiritual knowledge.

— The Bhagavad-Gita, ch. H.