There does not need to be an Article and Section in the Constitution which states the executive is NOT empowered to do a certain thing.
Our Constitution is structured in such a way that if a particular branch of our government is not empowered to do some certain thing, then that branch simply does not have the power to do that certain thing. It is not necessary for the Constitution to declare that it lacks that power.
So what empowers the President to appoint a cabinet?