Brahmapurana 220.21

Brahmapurāṇa 220.21

tena kāryaṃ caturdaśyāṃ teṣāṃ tṛptim abhīpsatā
śrāddhaṃ kurvann amāvāsyāṃ yatnena puruṣaḥ śuciḥ //