Evidence for God from Science

I think the Muslim is claiming that we are violating the first commandment because we believe in the trinity. I notice Muslims often emphasize that they believe in ONE God and accuse Christians of tritheism. So yes, the claim is that Christ is an idol and we are worshiping a man.

A Muslim friend of mine said that Exodus 20:1-6 (the first commandment) is proof that Jesus was merely a prophet. How would you defend your position as a Christian to this claim?