From Plato’s Republic (379b). A discussion between Socrates and Glaucon about whether or not an unjust man profits more than a just man. The following excerpt is Socrates speaking about whether good or evil is from God. I like the simplicity of Socrates’s logic and how he seems to be able to objectively come to an assertive conclusion.
Socrates: And is not God of course good in reality and always to be spoken of as such?
Socrates: But further, no good thing is harmful, is it?
Glaucon: By no means.
Socrates: Can that which does not harm do any evil?
Glaucon: Not that either.
Socrates: But that which does no evil would not be cause of any evil either?
Glaucon: How could it?
Socrates: Once more, is the good beneficent?
Socrates: It is the cause, then, of welfare?
Socrates: Then the good is not the cause of all things, but of things that are well it is the cause — of things that are ill it is blameless.
Glaucon: Entirely so
Socrates: Neither, then, could God, since he is good, be, as the multitude say, the cause of all things, but for mankind he is the cause of few things, but of many things not the cause. For good things are far fewer with us than evil, and for the good we must assume no other cause than God, but the cause of evil we must look for in other things and not in God.
Socrates doesn’t go so far as to declare the origin of evil, but that God must not be the source of it so we should look elsewhere. I like the objectivity in the logic above, regardless of what he may or not may believe about the gods.