SB 12.6.24

naiṣa tvayā manuṣyendra
 vadham arhati sarpa-rāṭ
anena pītam amṛtam
 atha vā ajarāmaraḥ
na — not; eṣaḥ — this snake-bird; tvayā — by you; manuṣya-indra — O great ruler of men; vadham — murder; arhati — deserves; sarpa-rāṭ — the king of snakes; anena — by him; pītam — has been drunk; amṛtam — the nectar of the demigods; atha — therefore; vai — certainly; ajara — free from the effects of old age; amaraḥ — virtually immortal.
O King among men, it is not fitting that this king of snakes meet death at your hands, for he has drunk the nectar of the immortal demigods. Consequently he is not subject to the ordinary symptoms of old age and death.