Srimad Bhagavatam Canto 08, Chapter 11, Text 39

SB 8.11.39

tam daivim giram akarnya
 maghavan susamahitah
dhyayan phenam athapasyad
 upayam ubhayatmakam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
After hearing the ominous voice, Indra, with great attention, began to meditate on how to kill the demon. He then saw that foam would be the means, for it is neither moist nor dry.
Srimad Bhagavatam Canto 08, Chapter 11, Text 38
Srimad Bhagavatam Canto 08, Chapter 11, Text 40