Shatapatha Brahmana 4.5.1.2

4.5.1.2

sa yadamutra rājānaṃ kreṣyannupapraiṣyanyajate | tasmāttatprāyaṇīyaṃ nāmātha yadatrāvabhṛthādudetya yajate tasmādetadudayanīyaṃ nāma tadvā etatsamānameva haviradityā eva prāyaṇīyamadityā udayanīyamiyaṃ hyevāditiḥ

And because, on that occasion, he offers when about to go forth (upa-pra-i) to buy the king (Soma), therefore that (opening oblation) is called Prâyanîya. And because he now offers after coming out (ud-â-i) from the expiatory bath, therefore this (concluding oblation) is called Udayanîya. For this indeed is one and the same oblation: to Aditi belongs the opening, to Aditi the concluding (oblation); for Aditi is this (earth).