Chāndogya Upaniṣad 3.7.3

3.7.3

sa ya etad evam amṛtaṃ veda rudrāṇām evaiko bhūtvendreṇaiva mukhenaitad evāmṛtaṃ dṛṣṭvā tṛpyati \
sa etad eva rūpam abhisaṃviśati \
etasmād rūpād udeti \\307.3\

3. He who knows thus that nectar becomes one of the Rudras themselves and through Indra as his mouth is satisfied merely with seeing that nectar. He enters that very form and comes forth from that form.