Bhagavad Gita 6.20

यत्रोपरमते चित्तं निरुद्धं योगसेवया |
यत्र चैवात्मनात्मानं पश्यन्नात्मनि तुष्यति

Translation

When the mind, restrained from material activities, becomes still by the practice of Yog, then the yogi is able to behold the soul through the purified mind, and he rejoices in the inner joy.