Matsyapurana 47.36

47.36

balinādhiṣṭhite caiva purā lokatraye kramāt
sakhyamāsītparamakaṃ devānāmasuraiḥ saha //

Sûta said:—At the end of a Yuga, and when morals of the time becomes lax, owing to the loss of righteousness in the universe, Lord Viṣṇu casts off His Divine form and assumes that of a man; or, when the Devas and the Asuras combine to oppress the world, then the Lord Hari incarnates Himself. Thus he incarnated when, in the days gone by, the Daitya Hiraṇya Kaśyapu was ruling the three worlds. Similarly, He incarnated when Bali of yore ruled the three worlds. In the reigns of these two rulers there was great friendship between the Devas and the Asuras.—34-36.