Shatapatha Brahmana 4.3.1.17

4.3.1.17

upayāmagṛhīto 'si | iṣe tvetyevādhvaryurgṛhṇātyupayāmagṛhīto 'syūrje tveti pratiprasthātaitāveva śāradau sa yacaradyūrgrasa oṣadhayaḥ pacyante teno haitāviṣaścorjaśca

With 'Thou art taken with a support: thee for Ish (sap)!' the Adhvaryu draws (the seventh); with 'Thou art taken with a support: thee for Ûrg (food)!' the Pratiprasthâtri (the eighth). These two are the autumn (months): because in autumn food (ûrg) and juice, (namely) plants, ripen, therefore these two are Isha and Ûrga.