Shatapatha Brahmana 9.5.2.8

9.5.2.8

saptarcam bhavati | saptacitiko 'gniḥ sapta 'rtavaḥ sapta diśaḥ sapta devalokāḥ sapta stomāḥ sapta pṛṣṭhāni sapta candāṃsi sapta grābhyāḥ paśavaḥ saptāraṇyāḥ sapta śorṣanprāṇā yatkiṃ ca saptavidhamadhidevatamadhyātmaṃ tadenena sarvamāpnoti tā anuṣṭubhamabhisampadyante vāgvā anuṣṭubvācaivāsya tadāpnoti yadasya kiṃ cānāptam

It is (a hymn) of seven verses,--the fire-altar consists of seven layers, (and there are) seven seasons, seven regions, seven worlds of the gods, seven stomas, seven prishtha (sâmans), seven metres, seven domestic animals, seven wild ones, seven vital airs in the head, and whatever else there is of seven kinds, relating to deities and relating to the self,--all that he thereby secures. They become equal to the Anushtubh, for the Anushtubh is speech, and it is by speech that he secures for him (Agni) all that which is not yet secured for him.