Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.3.8

13.3.3.8

dvādaśa evāgniḥ syāt ekādaśa yūpā yaddvādaśo'gnirbhavati dvādaśa māsāḥ saṃvatsaraḥ saṃvatsarameva yajñamāpnoti yadekādaśa yūpā virāḍvā eṣā sammīyate yadekādaśinī tasyai ya ekādaśa stana evāsyai sa duha evaināṃ tena

There may, indeed, be a twelvefold altar, and eleven stakes. When the altar is a twelvefold one--twelve months being a year--it is the year, the sacrifice, he obtains. When there are eleven stakes, then that Virâg (metre), the Ekâdasinî, is contrived; and that which is its eleventh (stake) is its teat: thereby he milks it.