Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.3.17

2.3.3.17

atha yāmetāṃ samidhamabhyādadhāti seṣṭakā yena mantreṇa juhoti tadyajuryenaitāmiṣṭakāmupadadhāti yadā vā iṣṭakopadhīyate 'thāhutirhūyate tadasyopahitāsveveṣṭakāsvetā āhutayo hūyante yā etā agnihotrāhutayaḥ

And again, the stick which he puts on the fire (corresponds to) a brick, and the formula wherewith he offers is the Yagus-text wherewith he puts on that brick; and when the brick is put on, then a libation is made: hence those same libations of the Agnihotra are offered on his pile of bricks.