Anandakanda 1.12.83

1.12.83

evaṃ kuryātprayatnena caikaviṃśativāsaram /
tena vajraśarīraḥ syādvalīpalitavarjitaḥ //

He should do this with effort for twenty-one days; / by this, his body becomes adamantine, free from wrinkles and grey hair;