Śatapatha Brāhmaṇa ("of a hundred paths") 3.7.1.15

3.7.1.15

atha minoti | yā te dhāmānyuśmasi gamadhyai yatra gāvo bhūriśṛṅgā ayāsaḥ atrāha tadurugāyasya viṣṇoḥ paramam padamavabhāri bhūrītyetayā triṣṭubhā minoti vajrastriṣṭubvajro yūpastasmāttriṣṭubhā minoti

He then plants it (in the hole) with (Vâg. S. VI, 3), 'To what resorts of thine we long to go where are the swift-footed, many-horned kine; there, forsooth, was imprinted wide-striding Vishnu's highest mighty foot-step.' With this trishtubh verse he plants it; the trishtubh is a thunderbolt, as the sacrificial stake is a thunderbolt; therefore he plants it with a trishtubh verse.