Shatapatha Brahmana 8.4.2.14

8.4.2.14

atha 'rtavye upadadhāti | ṛtava ete yadṛtavye ṛtūnevaitadupadadhāti sahaśca sahasyaśca haimantikāvṛtū iti nāmanī enayorete nāmabhyāmevaine etadupadadhāti dve iṣṭake bhavato dvau hi māsāvṛtuḥ sakṛtsādayatyekaṃ tadṛtuṃ karoti

He then lays down two Ritavyâs (seasonal bricks);--the seasonal ones being the same as the seasons, it is the seasons he thus lays down;--with (Vâg. S. XIV, 27), 'Saha and Sahasya, the two winter-seasons!' These are the names of those two, it is with their names he thus lays them down. There are two such bricks, for a season consists of two months. Only once he settles them: he thus makes (the two months) one season.