Bhagavad Gita 4.38
There is nothing in the world so purifying as wisdom; and he who is a perfect saint finds that at last within himself.
न हि ज्ञानेन सदृशं पवित्रमिह विद्यते।
तत्स्वयं योगसंसिद्धः कालेनात्मनि विन्दति॥na hi jñānena sadṛśaṃ pavitramiha vidyate|
tatsvayaṃ yogasaṃsiddhaḥ kālenātmani vindati||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).