The Iliad 8.127–138

Then had ruin come and deeds beyond remedy been wrought, and they had been penned in Ilios like lambs, had not the father of men and gods been quick to see. He thundered terribly and let fly his white lightning-bolt, and down before the horses of Diomedes he hurled it to earth; and a terrible flame arose of burning sulphur, and the two horses, seized with terror, cowered beneath the car. Then from the hands of Nestor slipped the shining reins, and he waxed afraid at heart, and spake to Diomedes: Son of Tydeus, come now, turn thou in flight thy single-hooved horses.Seest thou not that victory from Zeus waited not on thee? Now to yon man doth Zeus, the son of Cronos, vouchsafe glory for this day; hereafter shall he grant it also to us, if so be he will. But a man may in no wise thwart the purpose of Zeus, be he never so valiant; for in sooth he is mightier far.