Mbh 3.188.1c

Regenerate Brahmanas that have thoroughly studied the Vedas, that have tranquillity in their souls, they that have subdued their wrath, obtain a high reward by means of their numerous sacrifices. That reward, however, is unattainable by men that are wicked in their deeds, overwhelmed by covetousness, mean and disreputable with souls unblessed and impure. Therefore, must thou know, O Brahmana that this reward which is obtained by persons having their souls under control and which is unobtainable by the ignorant and the foolish,--this which is attainable by asceticism alone,--is productive of high merit. And, O best of men, at those times when virtue and morality decrease and sin and immorality increase, I create myself in new forms. And, O Muni, when fierce and malicious Daityas and Rakshasas that are incapable of being slain by even the foremost of the gods, are born on earth, I then take my birth in the families of virtuous men, and assuming human body restore tranquillity by exterminating all evils. Moved by my own maya, I create gods and men, and Gandharvas and Rakshasas, and all immobile things and then destroy them all myself (when the time cometh). For the preservation of rectitude and morality I assume a human form, and when the season for action cometh, I again assume forms that are inconceivable. In the Krita age I become white, in the Treta age I become yellow, in the Dwapara I have become red and in the Kali age I become dark in hue, I the Kali age, the proportion of immorality becometh three-fourths, (a fourth only being that of morality). And when the end of the Yuga cometh, assuming the fierce form of Death, alone I destroy all the three worlds with their mobile and immobile existences. With three steps, I cover the whole Universe; I am the Soul of the universe; I am the source of all happiness; I am the humbler of all pride; I am omnipresent; I am infinite; I am the Lord of the senses; and my prowess is great.