Devibhagavatapurana 4.25.31

4.25.31

jagrāha putrakāmastu muṇḍī daṇḍī babhūva ha |
ugraṃ tatra tapastepe māsamekaṃ phalāśanaḥ ||

In the first month He subsisted on fruits only and meditated on S’iva and repeated silently the S’iva mantra. Thus He practised very severe austerities. In the second month He subsisted on water only and stood on only one leg. In the third month he lived on air only and stood on the end of His great toe.