Agnipurana 184.2

184.2

kṛṣṇāṣṭamīvrataṃ vakṣye māse mārgaśire caret /
naktaṃ kṛtvā śucirbhūtvā gomūtraṃ prāśayenniśi //

I shall declare the votive observance of the dark eighth lunar day. One should perform it in the month of Mārgaśīrṣa: / having taken only an evening meal and having become pure, one should consume cow urine at night.