Shatapatha Brahmana 10.5.5.10

10.5.5.10

ūrdhvo vā eṣa etaccīyate yaddarbhastambo logeṣṭakāḥ puṣkaraparṇaṃ rukmapuruṣau srucau svayamātṛṇā dūrveṣṭakā dviyajū retaḥsicau viśvajyotirṛtavye aṣāḍhā kūrmo'tha hāsyaitadeva pratyakṣatamāṃ śiro yaścite'gnirnidhīyate tasmānna nirūhet

Upwards, indeed, he (Agni) is built up, to wit, (in the shape of) the grass-bunch, the clod-bricks, the lotus-leaf, the gold plate and man, the two spoons, the naturally-perforated one, the grass-brick, the Dviyagus, the two Retahsik, the Visvagyotis, the two seasonal bricks, the Ashâdhâ, and the tortoise; and that fire which is placed on the altar-pile, assuredly, is then most manifestly his (Agni's) head: let him therefore not pull out (the head).