Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 5.2.30

5.2.30

tathā ha asya pūrva pakṣe vaiśvadevena iṣṭam bhavati / (Cāturmāsya)

Therefore the gods with their horses become delighted. Now the steeds are also the seasons; verily thus he delights the seasons. In that he sacrifices afterwards with the full moon offering, thus by him in the first half of the month is the Vaiçvadeva offered.