The rules for precision damage are kinda vague, and from as far as I can tell there's only a couple things that are actually considered precision. My question has two parts though, first where in the rules can I find more information about Precision Damage. Looking at the Core Rule book I could only find that sneak attack damage is precision damage and not multiplied on a crit.
Secondly, and more importantly if its not in the answer to the first part, where does it say how precision damage works against DR. I assumed that its type matched they type of whatever weapon caused it. So a silver weapon's sneak attack bypasses DR/silver, but a regular weapon's sneak attack doesn't. However, my DM said in a similar situation that it was a separate damage source and would not bypass DR even if the weapon did.
The actual situation that came up was we were fighting an incorporeal creature, which is immune to non-magic weapons (also crits which negate the sneak attack damage all together, but we found out about that later). Assuming that they were not immune though, he said that our rogue could not add in the sneak attack damage even though the weapon was magic. And unless I can show him where it is in the rules that's the way its going to be.
EDIT: I realize it is mentioned in the answer found here, but this is not what im asking:
I am specifically looking for where any of this actually is in the rule books. Which book is it and which section or page number.