Śatapatha Brāhmaṇa ("of a hundred paths") 10.5.2.21

10.5.2.21

tadāhuḥ eko mṛtyurbahavā3 ityekaśca bahavaśceti ha brūyādyadahāsāvamutra tenaiko'tha yadiha prajāsu bahudhā vyāviṣṭasteno bahavaḥ

Now this Agni (fire-altar) consists of three bricks,--the Rik being one, the Yagus another, and the Sâman another: whatever (brick) he lays down here with a rik (verse) that has the gold plate for its foundation; whatever (brick he lays down) with a yagus (formula) that has the (gold) man for its foundation; and whatever (brick he lays down) with a sâman (hymn-tune) that has the lotus-leaf for its foundation. Thus he consists of three bricks.