Śatapatha Brāhmaṇa ("of a hundred paths") 10.2.1.11

10.2.1.11

atha sahasramityālikhitā uttarata upadadhāti tadyānīmāni vayasa uttarato vakrāṇi lomāni tāni tatkaroti sahasreṇa sarvaṃ vai sahasraṃ sarveṇaivāsminnetadrūpamuttamaṃ dadhāti tribhiḥ sahasraistrivṛdagniryāvānagniryāvatyasya mātrā tāvataivāsminnetadrūpamuttamaṃ dadhāti

On the left side he then lays down the one thousand (bricks) marked thus (from right to left): he thereby gives to it those curved plumes on the left side of the bird. With a thousand (bricks he does it each time)--a thousand means everything: with everything (required) he thus confers that highest form upon him (Agni);--with three thousand--Agni is threefold: as great as Agni is, as great as is his measure, with so much he thus confers the highest form upon him.