Mbh 13.85.8a

"'"'The Deities said, "There is an Asura of the name of Taraka who has been filled with pride in consequence of the boon he has obtained from Brahman. Through his energy he is able to oppose and discomfit us. Do thou ordain his destruction. O sire, do thou rescue these deities, these Prajapatis, and these Rishis, O highly blessed Pavaka! O puissant one, do thou beget a heroic son possessed of thy energy, who will dispel, O bearer of sacrificial libations, our fears from that Asura. We have been cursed by the great goddess Uma. There is nothing else than thy energy which can be our refuge now. Do thou, therefore, O puissant deity, rescue us all." Thus addressed, the illustrious and irresistible bearer of sacrificial libations answered, saying, "Be it so", and he than proceeded towards Ganga otherwise called Bhagirathi. He united himself in (spiritual) congress with her and caused her to conceive. Verily, in the womb of Ganga the seed of Agni began to grow even as Agni himself grows (when supplied with fuel and aided by the wind). With the energy of that god, Ganga became exceedingly agitated at heart. Indeed, she suffered great distress and became unable to bear it. When the deity of blazing flames cast his seed endued with great energy into the womb of Ganga, a certain Asura (bent on purposes of his own) uttered a frightful roar. In consequence of that frightful roar uttered by the Asura for purposes of his own (and not for terrifying her), Ganga became very much terrified and her eyes rolled in fear and betrayed her agitation. Deprived of consciousness, she became unable to bear her body and the seed within her womb. The daughter of Jahnu, inseminated with the energy of the illustrious deity, began to tremble. Overwhelmed with the energy of the seed she held in her womb, O learned Brahmana, she then addressed the deity of blazing fire, saying, "I am no longer capable, O illustrious one, of bearing thy seed in my womb.