I don't remember it being said.
I don't think it was in a book.
Way back in Storm Front, Bob tosses a vial across a circle and it is not disrupted. Because Bob does not have free will. It's not the object, it's the willful act of intending to throw physical matter across the circle. E.G. Molly in Peace Talks.
I think that's probably just "early installment weirdness."
