Śatapatha Brāhmaṇa ("of a hundred paths") 6.1.2.18

6.1.2.18

sa yaḥ sa prajāpatirvyasraṃsata | saṃvatsaraḥ so 'tha yā asyaitāḥ pañca tanvo vyaśraṃsanta 'rtavaste pañca vā ṛtavaḥ pañcaitāścitayastadyatpañca citīścinotyṛtubhirevainaṃ taccinoti yaccinoti tasmāccitayaḥ

And that Pragâpati who became relaxed is the year; and those five bodily parts of his which became relaxed are the seasons; for there are five seasons, and five are those layers: when he builds up the five layers, he thereby builds him up with the seasons; and inasmuch as he builds up (lays down), therefore they are layers.