Metaphysics (1.3.3-1.3.7)

Most of the earliest philosophers conceived only of material principles as underlying all things. That of which all things consist, from which they first come and into which on their destruction they are ultimately resolved, of which the essence persists although modified by its affections—this, they say, is an element and principle of existing things. Hence they believe that nothing is either generated or destroyed, since this kind of primary entity always persists. Similarly we do not say that Socrates comes into being absolutely when he becomes handsome or cultured, nor that he is destroyed when he loses these qualities; because the substrate, Socrates himself, persists.

In the same way nothing else is generated or destroyed; for there is some one entity (or more than one) which always persists and from which all other things are generated.

All are not agreed, however,

There are some[*] who think that the men of very ancient times, long before the present era, who first speculated about the gods, also held this same opinion about the primary entity. For they[*] represented Oceanus and Tethys to be the parents of creation, and the oath of the gods to be by water— Styx,[*] as they call it. Now what is most ancient is most revered, and what is most revered is what we swear by.