Manava Dharmashastra 6.20

6.20

cāndrāyaṇavidhānair vā śuklakṛṣṇe ca vartayet
pakṣāntayor vāpy aśnīyād yavāgūṃ kvathitāṃ sakṛt //

Or he may live according to the rule of the lunar penance (Kandrayana, daily diminishing the quantity of his food) in the bright (half of the month) and (increasing it) in the dark (half); or he may eat on the last days of each fortnight, once (a day only), boiled barley-gruel.