Vaishnava Dharmashastra 49.3

49.3

vratam etat saṃvatsaraṃ kṛtvā pāpebhyaḥ pūto bhavati ||

By performing this rite (on the twelfth day of the bright half of every month, from the month Mârgasîrsha to the month Kârttika) for one year, he is purified from every sin.