Anushasana Parva 108.19

As strength without exertion, or exertion without strength can never perform anything, singly, and as these, when combined, can do all things, so one that becomes gifted 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 acquires success. That purity which is derived from both sources is the best.