His justice cannot be impeached, because he infuseth no evil, enforceth to no evil, only ordaineth what shall be; his goodness cannot be impeached for suffering things which he can turn to such advantage for his own glory and the creature’s good. And, therefore, as the sun shineth upon a dunghill without having his beams polluted by it, so God’s ordination taketh in the sin of the creatures without any blemish to itself. God’s decrees are immanent in himself, working nothing that is evil in the creatures. Other things might be said, but I would not perplex the matter.
-Thomas Manton; works, volume 3, page 374
The Puritan's Woodshop 
My favorite quote regarding the existence of evil versus the goodness of God:
“To show that the fact of evil is inconsistent with the omnipotence of God, one would have to show that a world in which evil could not come into actuality would be richer in moral and spiritual values than a world in which moral freedom may actually be exercised and the exceeding sinfulness of sin may be known in the concrete.”
J.O. Buswell, Systematic Theology, Vol. 1, page 63, Zondervan Publishing House, 1962
Ah, yes. Very good!
How do we know dry without wet, or light without dark, and even good without evil. The rainbow itself is a testimony of this. There is a variety of color in the infallible promises of God.
Thanks for the quote Interface!