Revākhaṇḍa ascribed to the Vāyupurāṇa (RKV) 73.10

73.10

savatsā taruṇī śubhrā bahukṣīrā savastrakā /
kṛṣṇapakṣe caturdaśyām aṣṭamyāṃ vā pradāpayet //

One should cause [a cow] with a calf, young, white, yielding abundant milk, and draped with cloth, / to be given on the fourteenth or the eighth day of the dark fortnight.