SB 8.11.38

mayāsmai yad varo datto
 mṛtyur naivārdra-śuṣkayoḥ
ato ’nyaś cintanīyas te
 upāyo maghavan ripoḥ
Word for word: 
mayā — by me; asmai — unto him; yat — because; varaḥ — a benediction; dattaḥ — has been granted; mṛtyuḥ — death; na — not; eva — indeed; ārdra — by either a moist; śuṣkayoḥ — or by a dry medium; ataḥ — therefore; anyaḥ — something else, another; cintanīyaḥ — has to be thought of; te — by you; upāyaḥ — means; maghavan — O Indra; ripoḥ — of your enemy.
Translation: 
The voice also said, “O Indra, because I have given this demon the benediction that he will never be killed by any weapon that is dry or moist, you have to think of another way to kill him.”