Mbh 3.171.2

‘Beholding that excellent city, superior to the city of the celestials themselves, I asked Matali, saying, ‘Why do not the celestials reside in such (a place)? Surely, this appeareth superior to the city of Purandara.’ Thereat, Matali said, ‘In days of yore, O Partha, even this was the city of our lord of the celestials. Afterwards the celestials were driven from hence by the Nivata-Kavachas. Having performed the most rigid austerities, they had gratified the Grand-father and had asked (and obtained) the boons--namely, that they might reside here, and that they might be free from danger in wars with the gods.’ Then Sakra addressed the self-create lord saying, ‘Do thou, O lord, desirous of our own welfare do what is proper.’ Thereupon, O Bharata, in this matter the Lord commanded (Indra), saying, ‘O slayer of foes, in another body, even thou shalt be (the destroyer of the Danavas).’ Then, in order to slaughter them, Sakra rendered unto thee those weapons. The gods had been unable to slay these, who have been slain by thee. O Bharata, in the fullness of time, hadst thou come hither, in order to destroy them and thou hast done so. O foremost of men, with the object that the demons might be killed, Mahendra had conferred on thee the excellent prime energy of these weapons.’