Śatapatha Brāhmaṇa ("of a hundred paths") 7.3.1.25

7.3.1.25

tā etā yajuṣmatya iṣṭakāḥ | tā ātmannaivopadadhāti na pakṣapuceṣvātmanhyeva yajuṣmatya iṣṭakā upadhīyante na pakṣapuceṣu

These same (clods) are bricks having special prayers (yagushmatî): on the body (of the altar) he places them, not on the wings and tail; for bricks having special prayers are placed on the body, not on the wings or tail.