De Somniis (lib. i-ii)

But some have not only put themselves forward as rivals to human virtue, but have proceeded to such a pitch of folly as to oppose themselves also to divine virtue. Therefore Pharaoh, the king of the land of Egypt, is spoken of as the leader of the company which is devoted to the passions; for it is said to the prophet, "Behold, he is going forth to the river, and thou shalt stand in the way to meet him, on the bank of the river;" [*](Exodus vii. 15. )

for it is the peculiar characteristic of the one man to go forth to the rapidity and continual pouring forth of the irrational passion; and it is also characteristic of the wise man to oppose with exceeding vigour the arguments on behalf of pleasure and desire, not with his feet, but with his mind, firmly and immoveably, standing on the bank of the river; that is to say, on the mouth and on the tongue, which are the organs of speech. For standing firmly on these, he will be able to overturn and defeat the plausible specious arguments which advocate the cause of passion.