Prove that God doesn't exist.
Prove that science is infallible.
Prove that we evolved from other primates while those primates still exist in animal form.
Prove that the human race evolved from lower life forms even though realistic ancient art shows we have not changed for 10's of thousands of years (i.e. frescoes uncovered from Pompeii, or Egyptian art from the kingdom of Ahknaten).
Or better yet, that mummies and other remains found show we haven't changed either.
Tell me what you saw when you witnessed the moment of creation.
ETA: God is described as a superior being, the creator of the universe. If you say there is no God, that God did not create the universe, then you yourselves would have to be gods to know this. You can argue that you have seen no evidence of God, which does not discount that other's have; however, you can still say you don't believe...but you can never say God does not exist and have that be a true statement, because you are not omnisicent. In truth, if you do not believe in God, you can only say you don't feel that He exists - you can not, without a doubt, with certainty, nor definitively say that there is no God. Nor can you likewise dispute how this world and it's inhabitants came into being, and in their current state. Not unless you could prove you were there at the time of creation and to consciously, truthfully testify what actually happened.
Furthermore, due to the fallability of humans, and that science was created /employed by humans, science is imperfect. In regard to the theory of evolution, which directly goes against what would be a literal understanding of creation in the Bible, you could never say that evolution is a superior theory about creation versus Creationism. You could never say evolution is right and Creationism is wrong. You would also have to have been present at the time of creation to assert this as definitive truth.
For this reason, no one can ever say there is no God, and no one can ever say that God did not create Adam out of the earth.