Shatapatha Brahmana 10.2.5.15

10.2.5.15

atha trīṇyahānyupātiyanti yadahaḥ śatarudriyaṃ juhoti yadaharupavasatho yadahaḥ prasutastadyatteṣvahaḥsūpasadā caranti tāni tasya māsasyāhorātrāṇyatha yatpravargyeṇa tadu tasminnṛtāvādityam pratiṣṭhāpayatyetāvānvai trayodaśasu māseṣu kāmaḥ saptasvṛtuṣu tadyāvāṃstrayodaśasu māseṣu kāmaḥ saptasvṛtuṣu taṃ tatsarvamātmānamabhisaṃcinute

And in addition to these there are three days, to wit, the day on which he performs the Satarudriya offering, the day of preparation, and the day on which the Soma is pressed. When they perform the Upasad on these days, these (days) are the days and nights of that (thirteenth, or intercalary) month: and when (they perform) the Pravargya, he thereby establishes yonder sun also in that (seventh) season,--so long, indeed, desire (lasts) in the thirteen months and the seven seasons: he thus builds for himself a body so as to obtain all of whatever desire there is in thirteen months and seven seasons.