Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.16

7.4.2.16

atha dviyajuṣamupadadhāti | indrāgnī akāmayetāṃ svargaṃ lokamiyāveti tāvetāmiṣṭakāmapaśyatāṃ dviyajuṣamimāmeva tāmupādadhātāṃ tāmupadhāyāsyai pratiṣṭhāyai svargaṃ lokamaitāṃ tathaivaitadyajamāno yaddviyajuṣamupadadhāti yena rūpeṇa yatkarma kṛtvendrāgnī svargaṃ lokamaitāṃ tena rūpeṇa tatkarma kṛtvā svargaṃ lokamayānīti sā yaddviyajurnāma dve hyetāṃ devate apaśyatāṃ yadveva dviyajuṣamupadadhāti yajamāno vai dviyajuḥ

He then puts down a Dviyagus (brick). Indra and Agni desired, 'May we go to the heavenly world!' They saw that dviyagus brick, even this earth, and laid it down; and having laid it down, they went to the heavenly world from that foundation. In like manner when this Sacrificer lays down a dviyagus (brick), (he does so) thinking, 'I want to go to the heavenly world by the same means (rûpa), by performing the same rite by which Indra and Agni went to the heavenly world!' And as to its being called 'dviyagus,' it is because two deities saw it. And as to why he lays down a dviyagus one: the dviyagus doubtless is the Sacrificer.