Śatapatha Brāhmaṇa ("of a hundred paths") 10.1.3.6

10.1.3.6

te devā abruvan amṛtamimaṃ karavāmeti tasyaitābhyāmamṛtābhyāṃ tanūbhyāmetām martyāṃ tanūm parigṛhyāmṛtāmakurvanniṣṭakācitibhyām purīṣacitiṃ tathā dvitīyāṃ tathā tṛtīyāṃ tathā caturthīm

The gods spake, 'Let us make him immortal!' Having encompassed that mortal form by those immortal forms of his, they made it immortal--the layer of earth by means of two layers of bricks: in like manner the second, the third, and the fourth (layers of earth).