Mbh 12.161.1a

"'Bhishma said, "They that are possessed of knowledge say that everything has penance for its root. That foolish person who has not undergone penances does not meet with the rewards of even his own acts. The puissant Creator created all this universe with the aid of penances. After the same manner, the Rishis acquired the Vedas through the power of penances. It was by the aid of penances that the Grandsire created food, fruit and roots. It is by penances that persons crowned with ascetic success behold the three worlds, with rapt souls. Medicines and all antidotes to injurious substances, and the diverse acts (seen here), produce their intended results through the aid of penance. The accomplishment of all purposes depends upon penance. Whatever things there are that are apparently unattainable are sure to be won by the aid of penance. Without doubt, the Rishis obtained their sixfold divine attributes through penance. A person that drinks alcoholic stimulants, one that appropriates the possessions of others without their consent, one guilty of foeticide, one that violates one's preceptor's bed, are all cleansed by penance properly practised. Penances are of many kinds. They exhibit themselves through various outlets. Of all kinds of penances, however, that one may practise after abstaining from pleasure and enjoyment, abstention from food is the highest and best. The penance involved in abstention from food is superior, O king, to even compassion, truthfulness of speech, gifts, and restraining the senses. There is no act more difficult to accomplish than gift. There is no mode of life that is superior to serving one's mother. There is no creature superior to those that are conversant with the three Vedas. Similarly, renunciation constitutes the highest penance. People keep their senses under control for taking care of their virtue and heaven.