Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.31

7.4.2.31

yadvevaite atropadadhāti | prajāpatireṣo 'gniḥsaṃvatsara u prajāpatistasya pratiṣṭhaiva prathamā citiḥ pratiṣṭho asya vasanta ṛtustadyadete atropadadhāti yadevāsyaite ātmanastadasminnetatpratidadhāti tasmādete atropadadhāti te anantarhite viśvajyotiṣa upadadhāti prajā vai viśvajyotiranantarhitāstatprajā ṛtubhyo dadhāti tasmātprajā ṛtūnevānuprajāyanta ṛtubhirhyeva garbhe santaṃ sampaśyantyutubhirjātam

And, again, why he now lays down these two;--this Agni is Pragâpati, and Pragâpati is the year; the first layer is his foundation, and the spring season also is his foundation;--thus when he now lays down these two (bricks), he thereby puts back into him what those two are to that body of his: this is why he now lays down those two (bricks). He lays them down close to the 'all-light' brick: the 'all-light' brick being progeny, he thus lays progeny close together with the seasons; whence progeny is produced in accordance with the seasons, for by seasons people compute (the age of man) whilst in the state of embryo, and by seasons when he is born.