Shatapatha Brahmana 6.3.1.11

6.3.1.11

tadyāni trīṇi prathamāni | ime te lokā atha yaccuturthaṃ yajustrayī sā vidyā jagatī sā bhavati jagatī sarvāṇi candāṃsi sarvāṇi candāṃsi trayī vidyātha yāni catvāryuttamāni diśastānīme ca vai lokā diśaśca prajāpatirathaiṣā trayī vidyā

The first three which there are, are these (three) worlds; and what fourth prayer there is that is the threefold science, that is the Gagatî,--the Gagatî being all the metres, and all the metres (making up) the threefold science; and what last four (prayers) there are, they are the quarters: now Pragâpati indeed is those worlds and the quarters; and that (gagatî verse in the middle) is the threefold science.