Scripture please?
There is none because praying to saints is not only not mentioned but is forbidden. You don't pray to dead people, even though their souls live on.
The Communion of Saints was not formed and their veneration established till the canon was closed. For scripture and reasoning supporting saint veneration in general, see Communion of Saints, a recent thread. Or just explain when, in your view, why intercession by Timothy on behalf od a king, commended by St. Paul in 1 Timothy 2, should stop should Timothy die.
is forbidden
Necromancy is forbidden, indeed, because the Church forbids it. Veneration of saints is encouraged because the Church encourages it.