Bhagavad Gita
4.38

न हि ज्ञानेन सदृशं पवित्रमिह विद्यते | तत्स्वयं योगसंसिद्धः कालेनात्मनि विन्दति ||३८||

na hi jñānena sadṛśhaṁ pavitram iha vidyate tat svayaṁ yoga-saṁsiddhaḥ kālenātmani vindati

Translation

In this world, there is nothing so sublime and pure as transcendental knowledge. Such knowledge is the mature fruit of all mysticism. And one who has become accomplished in the practice of devotional service enjoys this knowledge within himself in due course of time.

Interpretation

Nothing in existence equals knowledge as a purifier ('pavitram'). This knowledge is found within oneself ('ātmani vindati') through the ripening of spiritual practice ('yoga-saṁsiddha') over time. It cannot be rushed or purchased — it is the natural fruit of sincere, sustained practice.