Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.6.4

13.3.6.4

tadāhuḥ aśvastomīyam pūrvaṃ hotavyāṃ3 dvipadā3 iti paśavo vā aśvastomīyam puruṣo dvipadā yadaśvastomīyaṃ hutvā dvipadā juhoti tasmātpuruṣa upariṣṭātpaśūnadhitiṣṭhati

Concerning this they say, 'Is the Asvastomîya to be offered first, or the Dvipadâ?' The Asvastomîya, surely, is cattle, and the Dvipadâ is man: inasmuch as he performs the Dvipadâs after performing the Asvastomîya, man subsequently establishes himself amongst cattle.