Śatapatha Brāhmaṇa ("of a hundred paths") 7.3.2.1

7.3.2.1

āpyānavatībhyāmabhimṛśya | pratyetyātithyena pracaratyātithyena pracarya pravargyopasadbhyām pracarati pravargyopasadbhyām pracaryāthaitāṃ carmaṇi citiṃ samavaśamayanti tadyaccarmaṇi carma vai rūpaṃ rūpāṇāmupāptyai lomato loma vai rūpaṃ rūpāṇāmupāptyai rohite rohite ha sarvāṇi rūpāṇi sarveṣāṃ rūpāṇāmupāptyā ānaḍuhe 'gnireṣa yadanaḍvānagnirūpāṇāmupāptyai prācīnagnīve taddhi devatrā

Having smoothed (the sand) down with the two verses containing (the verb) 'to grow,' and returned (to the hall) he proceeds with the guest offering. Having performed the guest offering, he proceeds with the Pravargya and the Upasad. Having performed the Pravargya and the Upasad, they appease that (first) layer on the (red ox-)skin. And as to why on a skin: for the obtainment of the forms, the skin being outward form;--on the hairy side: for the obtainment of the forms, hair being outward form;--on a ruddy (skin): for the obtainment of all forms, all forms (colours being contained) in the ruddy;--on (the skin) of an ox: for the obtainment of Agni's forms, the ox being the same as Agni;--on (the skin spread) with the neck towards the east, for that (tends) godward.