Mahabharata Anushasna Parva Chapter 108:2

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 108:2 Knowledge is said to constitute the especial purity of the body. So also freedom from desire, and cheerfulness of mind. Purity of conduct constitutes the purity of the mind. The purity that one attains by ablutions in sacred waters is regarded as inferior. Verily, that purity which arises from knowledge, is regarded as the best. Those ablutions which one performs with a blazing mind in the waters of the knowledge of Brahma in the Tirtha called Manasa, are the true ablutions of those that are conversant with Truth. That man who is possessed of true purity of conduct and who is always devoted to the preservation of a proper attitude towards all, indeed, he who is possessed of (pure) attributes and merit, is regarded as truly pure. These that I have mentioned have been said to be the Tirthas that inhere to the body. Do thou listen to me as I tell thee what those sacred Tirthas are that are situate on the earth also. Even as especial attributes that inhere to the body have been said to be sacred, there are particular spots on earth as well, and particular waters, that are regarded as sacred. By reciting the names of the Tirthas, by performing ablutions there, and by offering oblations to the Pitris in those places, one's sins are washed off. Verily, those men whose sins are thus washed off succeed in attaining to heaven when they leave this world. In consequence of their association with persons that are righteous, through the especial efficacy of the earth itself of those spots and of particular waters, there are certain portions of the earth that have come to be regarded as sacred. The Tirthas of the mind are separate and distinct from those of the earth. That person who bathes in both attains to success without any delay. As strength without exertion, or exertion without strength can never accomplish anything singly, and as these, when combined, can accomplish all things, even so one that becomes endued with the purity that is contributed by the Tirthas in the body as also by that which is contributed by the Tirthas on the earth, becomes truly pure and attains to success. That purity which is derived from both sources is the best.