Hesiod, the Homeric Hymns, and Homerica

Muses of Pieria who give glory through song, come hither, tell of Zeus your father and chant his praise. Through him mortal men are famed or un-famed, sung or unsung alike, as great Zeus wills. For easily he makes strong, and easily he brings the strong man low; easily he humbles the proud and raises the obscure, and easily he straightens the crooked and blasts the proud,—Zeus who thunders aloft and has his dwelling most high.

Attend thou with eye and ear, and make judgements straight with righteousness. And I, Perses, would tell of true things.

So, after all, there was not one kind of Strife alone, but all over the earth there are two. As for the one, a man would praise her when he came to understand her; but the other is blameworthy: and they are wholly different in nature. For one fosters evil war and battle, being cruel: her no man loves; but perforce, through the will of the deathless gods, men pay harsh Strife her honour due. But the other is the elder daughter of dark Night, and the son of Cronos who sits above and dwells in the aether, set her in the roots of the earth: and she is far kinder to men. She stirs up even the shiftless to toil; for a man grows eager to work when he considers his neighbour, a rich man who hastens to plough and plant and put his house in good order; and neighbour vies with his neighbour as he hurries after wealth. This Strife is wholesome for men. And potter is angry with potter, and craftsman with craftsman, and beggar is jealous of beggar, and minstrel of minstrel.