Śatapatha Brāhmaṇa ("of a hundred paths") 6.7.2.10

6.7.2.10

atha viṣṇukramānkramate | etadvai devā viṣṇurbhūtvemāṃlokānakramanta yadviṣṇurbhūtvākramanta tasmādviṣṇukramāstathaivaitadyajamāno viṣṇurbhūtvemāṃlokānkramate

He then strides the Vishnu-strides. For the gods, in the form of Vishnu (the sun), then strode through these worlds; and inasmuch as, in the form of Vishnu, they thus strode, they are called the Vishnu-strides: in like manner does the Sacrificer, in the form of Vishnu, now stride through these worlds.