Shatapatha Brahmana 8.7.2.17

8.7.2.17

athāta iṣṭakāmātrāṇāmeva | pādamātrīḥ prathamāyāṃ cottamāyāṃ ca cityorupadadhyātpratiṣṭhā vai pādo yo vai pādaḥ sa hasta ūrvasthamātryo varṣiṣṭhāḥ syurna hyūrvasthātkiṃ cana varṣīyo 'sthyasti tryālikhitavatyastisraścitayaḥ syustrivṛto hīme lokā aparimitālikhite dve raso haite citī aparimita u vai rasaḥ sarvāstveva tryālikhitavatyaḥ syuḥ sarve hyeveme lokāstrivṛtaḥ

Now, then, of the measures of the bricks. In the first and last layers let him lay down (bricks) of a foot (square), for the foot is a support; and the hand is the same as the foot. The largest (bricks) should be of the measure of the thigh-bone, for there is no bone larger than the thigh-bone. Three layers should have (their bricks) marked with three lines, for threefold are these worlds; and two (layers may consist) of (bricks) marked with an indefinite number of lines, for these two layers are the flavour, and the flavour is indefinite; but all (the layers) should rather have (bricks) marked with three lines, for threefold are all these worlds.