Mbh 3.101.1a

“Lomasa said, ‘Armed with the Vajra then, and supported by celestials endued with great might, Indra then approached Vritra, who was then occupying the entire earth and the heaven. And he was guarded on all sides by huge-bodied Kalakeyas with upraised weapons resembling gigantic mountains with towering peaks. And the encounter that took place between the gods and the Danavas lasted for a short while and was, O chief of the Bharatas, terrific in the extreme, appalling as it did the three worlds. And loud was the clash of swords and scimitars upraised and warded off by heroic hands in course of those fierce encounters. And heads (severed from trunks) began to roll from the firmament to the earth like fruits of the palmyra palm falling upon the ground, loosened from their stalks. And the Kalakeyas armed with iron-mounted bludgeons and cased in golden mail ran against the gods, like moving mountains on conflagration. And the gods, unable to stand the shock of that impetuous and proudly advancing host, broke and fled from fear. Purandara of a thousand eyes, beholding the gods flying in fear and Vritra growing in boldness, became deeply dejected. And the foremost of gods Purandara, himself, agitated with the fear of the Kalakeyas, without losing a moment, sought the exalted Narayana’s refuge. And the eternal Vishnu beholding Indra so depressed enhanced his might by imparting unto him a portion of his own energy. And when the celestials beheld that Sakra was thus protected by Vishnu, each of them imparted unto him his own energy. And the spotless Brahmarshis also imparted their energies unto the chief of the celestials. And favoured thus by Vishnu and all the gods and by the high-blessed Rishis also, Sakra became mightier than before. And when Vritra learnt that the chief of the celestials had been filled with might of others, he sent forth some terrific roars.