Yāska's Nirukta 77.1.8

77.1.8

"ṣaḷara āhurarpitamiti ṣaḍṛtutayā" saṃvatsarasya stustiḥ | 'pañcapādaṃ' saṃvatsaram, ṛtavo hi saṃvatsarasya pādāḥ, tairasau patati gacchati | 'pitaraṃ' pālakaṃ sarvabhūtānāmutpādayitāraṃ vā 'dvādaśākṛtim' dvādaśamāsapravibhaktavigraham, "dvādaśamāsāḥ saṃvatsarasya" iti ca brāhmaṇam, 'divaḥ' dyulokasya 'pare' parame 'arddhe' sthāne yo'yamavasthita ādityaḥ, etasmin pañcapādaṃ pitaraṃ dvādaśākṛti 'purīṣiṇam' udakavantaṃ saṃvatsaram 'arpitamāhuḥ' aviśeṣeṇānye brāhmaṇāḥ | tasmāt sarva ṛtavo vṛṣṭimanta iti ha vijñāyate | tasmāt saṃvatsarasyodakavattvamupapadyate | 'atha' punaḥ 'ime' 'anye' ya ete 'upare' uparyavasthitāḥ, 'sapta' ṛṣayaḥ, ete 'vicakṣaṇaṃ' vividhānāṃ sarvabhūtakarmaṇāṃ draṣṭārametamādityaṃ 'cakre ṣaḷare' ṣaḍarre tasmin saṃvatsarākhye arpitamāhuḥ | athavā-saptacakra ādityaḥ, sa hi saptabhī raśmibhiścakrate dīpyate, 'saptacakre'- ityekaṃ pada tasmādevamapi bhavati || evameke saṃvatsarādityapratiṣṭhamāhuḥ, apare punarāditya saṃvatsarapratiṣṭhamityeṣa mantrastārthaḥ || evametasyāmṛci ādityasaṃvatsarau stūyete | vakṣyati, hi "candramasā vāyunā saṃvatsareṇevi saṃvatsaraḥ" | mavatsarasya cakrarūpakeṇa nābhyādibhiḥ stutirūpapadyate || "arāḥ pratyūtā nābhau" praॉnagatā ityarthaḥ || "ṣaṭ punaḥ sahateḥ" te hi pañcamasyāmabhibhūya vartante || "dvādaśāraṃ na hi tajjarāya"-iti | "dvādaśa pradhayaścakramekam" iti | "iti māsānām" 'etau pādau bhavataḥ' iti vākyaśeṣaḥ ||