Mbh 13.155.2a

"'Bhishma continued, "Thus addressed, king Arjuna remained silent. The god of wind once more said, 'Hear, O king, one of the great feats of the illustrious Vasishtha. Once on a time the deities were engaged in performing a sacrifice on the shores of the lake Vaikhanasa. Knowing of his puissance, the sacrificing gods thought of Vasishtha and made him their priest in imagination. Meanwhile, seeing the gods reduced and emaciated in consequence of the Diksha they were undergoing, a race of Danavas, of the name of Khalins, of statures as gigantic as mountains, desired to slay them. Those amongst the Danavas that were either disabled or slain in the fight were plunged into the waters of the Manasa lake and in consequence of the boon of the Grandsire they instantly came back to vigour and life. Taking up huge and terrible mountain summits and maces and trees, they agitated the waters of the lake, causing them to swell up to the height of a hundred yojanas. They then ran against the deities numbering ten thousand. Afflicted by the Danavas, the gods then sought the protection of their chief, Vasava. Sakra, however, was soon afflicted by them. In his distress he sought the protection of Vasishtha. At this, the holy Rishi Vasishtha assured the deities, dispelling their fears. Understanding that the gods had become exceedingly cheerless, the ascetic did this through compassion. He put forth his energy and burnt, without any exertion, those Danavas called Khalins. Possessed of wealth of penances, the Rishi brought the River Ganga, who had gone to Kailasa, to that spot. Indeed, Ganga appeared, piercing through the waters of the lake. The lake was penetrated by that river. And as that celestial stream, piercing through the waters of the lake, appeared, it flowed on, under the name of Sarayu. The place whereon those Danavas fell came to be called after them.