Śatapatha Brāhmaṇa ("of a hundred paths") 7.2.2.19

7.2.2.19

catasraḥ sītā yajuṣā kṛṣati | tadya ime śīrṣamścatvāro niruktāḥ prāṇāstānasminnetaddadhāti tadvai yajuṣāddhā vai tadyadyajuraddho tadyadime śīrṣanprāṇāḥ

Four furrows he ploughs with prayer: he thereby puts into him those four well-defined vital airs which are in the head; and this (he does) with prayer,--true is the prayer, and true (manifest, real) are these vital airs in the head.