Arabic sin and shin sounds in Classical times?

Question

What sounds did س and ش‎ make in (early) Classical Arabic?I have heard that maybe they were not [s] and [ʃ]. Is that a widely accepted truth? If that's true, what is the evidence for that?

Answer 1

There is no indication (to my knowledge) that س and ش were (ever) pronounced the same in Classical Arabic. They were, however, written the same as س until the dots were added well into the Umayyad period.