Srimad Bhagvata Mahapurana: Book 6: Chapter 11: Verses 1-13
Sri Suka went on : Frantic with fear-and robbed of (all) good sense, and intent on flight, the demons paid no heed at all to the advice of their chief, who was thus preaching virtue to them, O king (Pariksit) Roused to indignation and enraged to see the demon host being shattered and put to flight-as though it were masterless-by the gods (who pass through only three stages in life, viz., childhood, adolescence and full manhood and never grow old, and) to whom time (fortune) appeared propitious, Vrtra (the enemy of Indra), the foremost of the demons, felt agonized (at heart). Warding the gods off by his (own) might, O Pariksit, and scolding them, he actually addressed the following words to them:- "What will be gained by you through these fugitives-who are no better than the excreta of their mother-being struck from behind ? Indeed the slaughter of the terror-stricken is neither praiseworthy nor conducive to heavenly enjoyment for those who account themselves as brave. If you are keen about fighting or if there is courage in your heart, O vile creatures, and (again) if there is no craving (in your heart) for sensuous enjoyments, stand but for a moment before me". Thus threatening the host of gods, his enemies, by his (words as well as by his gigantic) figure, and full of rage, Vrtra, who was possessed of vast strength, roared in such a way that people fainted (to hear the sound). Rendered unconscious by that (terrible) yell of Vrtra, all the gods actually dropped on the ground just as they would when struck with lightning.
Taking up his spear and shaking the earth by his strength, Vrtra (whose ardent passion for the pastime of warfare could not be easily repressed) trod down under his feet the troops of the gods-(that were) lying unconscious with their eyes closed-even as a lordly elephant would trample down in its mad fury a bed of lotuses. Indra (the wielder of the thunderbolt) was seized with great indignation to see him and hurled a huge mace at his enemy, who was (now) rushing towards him. The demon (however) sportfully caught that most formidable weapon with his left hand even as it approached him. Roaring in fury, the said enemy of Indra, who was possessed of terrible prowess, struck on the head with that mace the elephant (Airavata) that bore the mighty Indra on its back. All those present on the battle-field admired this feat of his, O Pariksit ! Smitten with the mace hurled by Vrtra even like a mountain struct with lightning and much afflicted, Airavata along with Indra (mounted on its back) retreated to a distance of twenty-eight cubits, reeling and vomiting blood, its mouth broken. That noble soul (Vrtra) did not aim the mace for a second time at Indra, who felt dejected in mind and whose elephant was stunned (with the blow). (Meanwhile,) O king of kings, Indra, whose wounded elephant was rid of its pain by the (very) touch of his hand, that shed drops of nectar, stood (once more) before Vrtra. Seeing the aforesaid Indra (his own enemy and) the slayer of his (elder) brother (Viswarupa), standing (before him) armed with the thunderbolt and seeking a (single) combat with him, 0 king of kings, Vrtra was filled with grief and infatuation as he recollected that cruel and sinful deed of his adversary, and spoke laughing (as follows) :