Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 19.5.4

19.5.4

mukhata eva tat saṃvatsaram prīṇanti /

xix. 8. The Caturviṅça is the beginning of the year; therefore it is an Agniṣṭoma, for the Agniṣṭoma is the beginning of the sacrifices; verily thus at the beginning they delight the year. Some make it an Ukthya, for the equipoise of the sacrifice. It has the Caturviṅça Stoma; the half months of the year are twenty-four; verily (it serves) to obtain the year. There are in it three hundred and sixty Stotriyās; three hundred and sixty are the days of the year; verily (they serve) to obtain the year.