Srimad Bhagavatam Canto 06, Chapter 12, Text 23

SB 6.12.23

sri-suka uvaca
iti bruvanav anyonyam
 dharma-jijñasaya nrpa
yuyudhate maha-viryav
 indra-vrtrau yudham pati
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Sri Sukadeva Gosvami said: Vrtrasura and King Indra spoke about devotional service even on the battlefield, and then as a matter of duty they again began fighting. My dear King, both of them were great fighters and were equally powerful.
Srimad Bhagavatam Canto 06, Chapter 12, Text 22
Srimad Bhagavatam Canto 06, Chapter 12, Text 24