Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 5.5.26

5.5.26

tathā ha asya pūrva pakṣe varuṇa praghāsair iṣṭam bhavati / (Cāturmāsya)

and Ka is Prajāpati, verily thus he delights him; moreover the word Ka is a name of happiness; verily thus he confers happiness upon himself. In that he gives two pairing cattle, that is the symbol of propagation. In that he sacrifices to the steeds, the explanation of that has been given. In that he sacrifices to Varuṇa in the waters, verily thus he delights him in his own home. In that afterwards he sacrifices with the full moon sacrifice, thus in the first half of the month does he sacrifice with the Varuṇapraghāsas.