The Iliad 21.176–183

In the belly he smote him beside the navel, and forth upon the ground gushed all his bowels, and darkness enfolded his eyes as he lay gasping. And Achilles leapt upon his breast and despoiled him of his arms, and exulted saying: Lie as thou art! Hard is itto strive with the children of the mighty son of Cronos, albeit for one begotten of a River. Thou verily declarest that thy birth is from the wide-flowing River, whereas I avow me to be of the lineage of great Zeus. The father that begat me is one that is lord among the many Myrmidons, even Peleus, son of Aeacus; and Aeacus was begotten of Zeus.Wherefore as Zeus is mightier than rivers that murmur seaward, so mightier too is the seed of Zeus than the seed of a river. For lo, hard beside thee is a great River, if so be he can avail thee aught; but it may not be that one should fight with Zeus the son of Cronos. With him doth not even king Achelous vie,nor the great might of deep-flowing Ocean, from whom all rivers flow and every sea, and all the springs and deep wells; howbeit even he hath fear of the lightning of great Zeus, and his dread thunder, whenso it crasheth from heaven.