Skandapurana 6.3.62.7

6.3.62.7

vikhyātaṃ tu tadā loke pāpaghnaṃ pāṇḍunandana .
aṣṭamyāṃ ca caturdaśyāmubhau pakṣau ca bhaktitaḥ .
upoṣya śūlinaścāgre rātrau kurvīta jāgaram .. 62.7 ..

It became famous in the world, O son of Pāṇḍu, as destroying sin. / On the eighth and the fourteenth days of both fortnights, with devotion, / having fasted before the Trident-bearer, one should keep vigil at night, 62.7