I believe the passage I am looking for comes from Critique of Pure Reason. He says something to the effect that we are unable to understand how the representation of God can be both both totally wrathful and totally forgiving at the same time.
This is described in the last chapter of the Critique of Pure Reason, 'The History of Pure Reason'.
He there once again restates that (and why) all other conceivings of God before him had to be either sceptic or dogmatic, a common theme all over the last part.
I correct myself: In A631|B659-A642|670 he criticizes all theology out of speculative principles of reason and in effect explains why every determinination of God with the help of experience/intuition must fail (especially A636-8|B664-6). Your example isn't explicitely adressed, but can be subsumed under his criticism as I understand it.