By Satan you mean Mephistopheles, Beelzebub, Lucifer, The horned one, Old Nick, in short the Devil.
Tricky.
Perhaps the ultimate proof of the non-existence of God?

The argument goes something like this.

The origin of Evil

God made everything including the Devil.
The Devil is Evil
If god made the Devil without free will then he must have made him Evil in the first place.
Then God created Evil from himself therefore God is Evil.
But God is Good By definition.
Contradiction.
Therefore no God

If however God gave the Devil free will and the Devil chose Evil, God must have created Evil so that the Devil could make his choice.

Then God created Evil from himself therefore God is Evil.
But God is Good By definition.
Contradiction.
Therefore no God

QED

All the best PP