Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.11

6.2.2.11

yadveva vāyavyaḥ paśurbhavati | prājāpatyaḥ paśupuroḍāśo 'rdhaṃ ha prajāpatervāyurardham prajāpatistadyadubhau vāyavyau syātāmubhau vā prājāpatyāvardhaṃ haivāsya kṛtaṃ syānnārdhamatha yadvāyavyaḥ paśurbhavati prājāpatyaḥ paśupuroḍāśastena haivaitaṃ sarvaṃ kṛtsnam prajāpatiṃ saskaroti

And as to why the victim belongs to Vâyu, and the animal cake to Pragâpati;--one half of Pragâpati doubtless is Vâyu, and one half is Pragâpati: thus, were they both to belong to Vâyu, or both to Pragâpati, then only one half of him (Pragâpati) would be made up, and one half would not (be made up). But in that the victim belongs to Vâyu, and the animal cake to Pragâpati, thereby he puts together (restores) him, Pragâpati, wholly and entirely.