. . . show me in the U.S. Constitution where Income tax is constitutional.
I am not familiar with the U.S. Constitution, but I don't imagine that the constitution explicitly states that Income Tax is constitutational, or that any of the diverse and novel ways in which tax gets spent nowadays, such as "The War on Drugs", or "The War on Terror", or "welfare", are constitutional, for that matter. I do not believe that that the U.S. Constitution expressly says that it's not murder to kill unborn children either, but I believe that the US's Supreme Court has ruled that that astonishing conclusion is implicit in the Constitution.
I expect the Constitution, which I have never read, provides for the existence of an elected legislature, and that people in the past have voted for legislatures that have passed Acts that enable the raising of taxes, including Income Tax. Your remedies, if your don't like this, are to start a political party committed to the repeal of Income Tax enabling legislation, or to challenge that legislation in the Supreme Court. I think that if you pursue either remedy, you could find yourself kicking against the pricks of what God has ordained in providence. But please feel free to try. In the mean time, I hope you will pay your taxes like a good Christian.