Prove to U.S. citizens there is a law stating we must pay federal income taxes or face prosecution!

I have recently been on a hunt for a law stating that we as americans must pay federal income tax, not finding one , but finding former irs employees who simply quit their jobs due to no findings of laws they were forced to enforce. That being said I want and demand proof of such, if I have to pay the government to do their job , then I want a job done right