Agnipurana 184.1

184.1

agnir uvāca
brahmādimātṛyajanājjapen mātṛgaṇāṣṭamīṃ /
kṛṣṇāṣṭābhyāṃ caitramāse pūjyābdaṃkṛṣṇamarthabhāk //

Agni said: / From worshipping the Mothers headed by Brahmā, one should recite on the eighth day sacred to the host of Mothers. / Worshipping Kṛṣṇa on the dark eighth lunar day in the month of Caitra for a year, one gains prosperity.