Śatapatha Brāhmaṇa ("of a hundred paths") 10.2.6.1

10.2.6.1

saṃvatsaro vai prajāpatirekaśatavidhaḥ tasyāhorātrāṇyardhamāsā māsā ṛtavaḥ ṣaṣṭirmāsasyāhorātrāṇi māsi vai saṃvatsarasyāhorātrāṇyāpyante caturviṃśatirardhamāsāstrayodaśa māsāstraya ṛtavastāḥ śataṃ vidhāḥ saṃvatsara evaikaśatatamī vidhā

The one hundred and one-fold Pragâpati, doubtless, is the year, and thereto belong days and nights, half-months, months, and seasons. The days and nights of a month are sixty, and in the month, doubtless, the days and nights of the year are obtained; and there are twenty-four half-months, thirteen months, and three seasons (of four months)--that makes a hundred parts, and the year itself is the one hundred and first part.