SB 12.6.18

apaśyaṁs takṣakaṁ tatra
 rājā pārīkṣito dvijān
uvāca takṣakaḥ kasmān
 na dahyetoragādhamaḥ
Word for word: 
apaśyan — not seeing; takṣakam — Takṣaka; tatra — there; rājā — the King; pārīkṣitaḥ — Janamejaya; dvijān — to the brāhmaṇas; uvāca — said; takṣakaḥ — Takṣaka; kasmāt — why; na dahyeta — has not been burned; uraga — of all the serpents; adhamaḥ — the lowest.
Translation: 
When King Janamejaya did not see Takṣaka entering his sacrificial fire, he said to the brāhmaṇas: Why is not Takṣaka, the lowest of all serpents, burning in this fire?