The correct answer is the US Constitution.
In Article 1 Section 8 of the US Constitution, it clearly states that Congress has the ability to raise taxes. Raising taxes is an essential element of government, as it allows the government to fund programs like Medicare, Medicaid, Social Security, etc.
Before the US Constitution, Congress did not have the ability to tax. This caused financial issues for the federal government, as they did not have any new revenue. This is why Congress was given the ability to tax.