Shatapatha Brahmana 10.3.1.5

10.3.1.5

mano bṛhatīti tadya eva manaso mahimā yadvīryaṃ tadetatsahasram manasa evaitadvīryaṃ yaddhyasya cinvato mana utkrāmettata evaiṣo'gnirna cīyetaitenaivāsya rūpeṇa sahasrameṣa bṛhatīḥ saṃcito bhavati

'The Brihatî is the mind,'--thus, whatever power, whatever vigour there is in the mind that is this one thousand; and to the mind, indeed, this vigour belongs, for were the mind of him who builds it to pass away, this fire altar, assuredly, would not be built: by this its form that (altar) becomes built (so as to contain) a thousand Brihatîs.