Vaishnava Dharmashastra 89.3

89.3

tasmāt tu kārttikaṃ māsaṃ bahiḥsnāyī gāyatrījapanirataḥ sakṛd eva haviṣyāśī saṃvatsarakṛtāt pāpāt pūto bhavati ||

Therefore is that man purified from every sin committed during the past year, who persists during the month Kârttika in bathing (daily) out of the village, in muttering the Gâyatrî, and in taking a single meal each day, consisting of food fit for oblations.