Durga in the Devimahatmyam
(2.2) Long ago, when Mahisha was chief of the asuras [demons] and Indra was chief of the gods, there was a war between their forces for a full hundred years. The valorous asuras vanquished the army of the gods and, after all were conquered, Mahisha became the lord of heaven. Then led by Brahma, the lord of beings, the defeated gods went to Vishnu and Shiva and related in detail what had happened. [...]
When Vishnu and Shiva heard the entreaties of the gods, they knit their brows in fury and contorted their faces, whereupon a great radiance came forth from Vishnu’s rage-filled countenance, and so, too, from Brahma’s and Shiva’s. And from Indra’s body and from the bodies of all the other gods, a very great light issued, and it united and became one. The gods saw before them a peak of light like a mountain, blazing brightly and pervading the sky in every direction with its flames. Unequaled light, born from the bodies of all the gods, coalesced into a female form and pervaded the three worlds with its splendour. [...]
Then the gods bestowed on her their own weapons and adornments. From his trident Shiva drew forth another and gave it to her, and Vishnu bestowed a discus spun out from his own. Varuna gave her a conch; and Agni, the eater of oblations, gave her a spear. Vayu, the wind god, presented a bow and two quivers filled with arrows. Extracting a thunderbolt from his own, Indra, the lord of the immortals, the all-seeing one, gave it along with a bell from his elephant Airavata. From his staff of death Yama produced another staff, and Varuna, the lord of waters, gave a noose. Brahma, the lord of beings, gave prayer beads and an ascetic’s waterpot. Surya, the bringer of day, bestowed his rays of sunlight on all the pores of her skin; and Kala, the lord of time, presented a sword and shining shield. [...]
Honored also by the other gods with adornments and weapons, the Devi laughed thunderously and defiantly again and again. She filled the entire sky with her terrible roar, and from the immeasurable din a great echo resounded. All the worlds shook, and the oceans churned. The earth quaked, and the mountains heaved. [...] (Devimahatmyam, 2.2-2.34, translated by Devadatta Kali)
Once endowed with the god’s weapons, Durga throws herself into the battle against Mahisha’s armies. Once his armies and generals are defeated, Mahisha transforms himself into a giant buffalo. The duel with the great goddess then begins.
(3.25) [...] Mahisha, great in valour, struck the earth angrily with his hooves, flung mountains skyward with his horns, and bellowed frightfully. Under his frenzied wheeling, the trampled earth broke apart. Lashed by his tail, the ocean overflowed all around. Trashed by his horns, the clouds fragmented and dispersed. Tossed about on his blasting breath, mountains by the hundred fell from the sky.
When she saw the great asura approaching, inflated with rage, Candika [Durga] aroused her wrath and prepared to slay him. She threw her noose over him and bound him. Fettered thus in fierce battle, the great asura left his buffalo form and assumed the shape of a lion. No sooner had Ambika [Durga] severed his head than he appeared as a man with a sword in hand. Instantly, with her arrows the Devi cut him to shreds along with his sword and shield. Then he took the form of a great elephant [...]. The Devi chopped off his trunk with her sword. Once more the great asura assumed his buffalo form and caused the three worlds, with all that is moving and unmoving, to tremble.
Angered, Candika [Durga], the mother of the worlds, drank a divine potion, and with eyes reddened she laughed again and again. The asura bellowed in return, intoxicated with his own might and valour, and with his horns he hurled mountains at Candika. [...] She leapt upon the great asura, pinned his neck down with her foot, and pierced him through with her spear. Trapped under the Devi’s foot and crushed by her might, he emerged half-way in his true form from his buffalo mouth. Half-revealed and fighting still, that great asura fell to the Devi, beheaded by her great sword.
[...] Together with the great heavenly seers, the gods praised the Devi [Durga], the celestial musicians sang, and throngs of cloud-nymphs danced. (Devimahatmyam, 3.25-3.44, translated by Devadatta Kali).