Śatapatha Brāhmaṇa ("of a hundred paths") 1.6.2.1

1.6.2.1

yajñena vai devāḥ | imāṃ jitiṃ jigyuryaiṣāmiyaṃ jitiste hocuḥ kathaṃ na idam manuṣyairanabhyārohyaṃ syāditi te yajñasya rasaṃ dhītvā yathā madhu madhukṛto nirdhayeyurviduhya yajñaṃ yūpena yopayitvā tiro 'bhavannatha yadenenāyopayaṃstasmaddyūpo nāma tadvā ṛṣīṇāmanuśrutamāsa

Verily, by means of the sacrifice the gods made that conquest (of the world of heaven). When they had conquered, they said, 'How may this (celestial region) be made unattainable by men?' They then sipped the sap of the sacrifice, as bees would suck out honey; and having drained the sacrifice and effaced the traces of it with the (sacrificial) post, they concealed themselves: and because they effaced (ayopayan, viz. the sacrifice) with it, therefore it is called yûpa (sacrificial post). Now this was heard by the Rishis: