Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.2.2

6.3.2.2

so 'śvamabhimantrayate | praturtaṃ vājinnādraveti yadvai kṣipraṃ tattūrtamatha yatkṣiprātkṣepīyastatpratūrta variṣṭhāmanu saṃvatamitīyaṃ vai variṣṭhā saṃvadimāmanu saṃvatamityetaddivi te janma paramamantarikṣe tava nābhiḥ pṛthivyāmadhi yoniriditi tadenametā devatāḥ karotyagniṃ vāyumādityaṃ tadaśve vīryaṃ dadhāti

He addresses the horse, with (Vâg. S. XI, 12), 'Most speedily, O courser, run hither,'--what is swift, that is speedy, and what is swifter than swift, that is most speedy;--'along the widest range,'--the widest range doubtless is this (earth): thus, 'along this wide range;'--'in the sky is thy highest home, in the air thy navel, upon earth thy womb:' he thus makes it to be those deities, Agni, Vâyu, and Âditya (the sun), and thus lays vigour into the horse.