Śatapatha Brāhmaṇa ("of a hundred paths") 7.5.2.18

7.5.2.18

athottarato 'śvam | vātasya jūtimiti vātasya vā eṣa jūtiryadaśvo varuṇasya nābhimiti vāruṇo hyaśvo 'śvaṃ jajñānaṃ sarirasya madhya ityāpo vai sariramapsujā u vā aśvaḥ śiśuṃ nadīnāṃ harimadribudhnamiti girirvā adrirgiribudhnā u vā āpo 'gne mā hiṃsīḥ parame vyomannitīme vai lokāḥ paramaṃ vyomaiṣu lokeṣvenam mā hiṃsīrityetat

Then on the left side (he puts the head of) the horse, with (Vâg. S. XIII, 42), 'The speed of the wind,'--this one, the horse, is indeed the speed of the wind;--'Varuna's navel'--for the horse is Varuna;--'the horse, born in the midst of the flood;' the flood is the water, and the horse is indeed the water-born;--'the tawny, rock-founded child of rivers;' rock means mountain, and the waters are indeed founded on the mountains;--'harm him not, Agni, in the highest region!' the highest region means these worlds: thus, do not harm him in these worlds!