Chandogya Upanishad 3.10.3

3.10.3

sa ya etad evam amṛtaṃ veda sādhyānām evaiko bhūtvā brahmaṇaiva mukhenaitad evāmṛtaṃ dṛṣṭvā tṛpyati \
sa etad eva rūpam abhisaṃviśati \
etasmād rūpād udeti \\310.3\

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