Question

You said, and have also written more than once, that “when a person acts outside his halakhic territory on the basis of a halakhic consideration (which is legitimate within that domain), then the prohibition may indeed be overridden (by virtue of that consideration), and therefore if he does so he may perhaps not violate the prohibition of theft, but the boundary of his halakhic territory still remains in place, since it does not depend on any halakhic considerations, and there is here an extra-halakhic prohibition of crossing a meta-halakhic boundary.”
That is very wonderful, but I don’t understand, or don’t feel, or don’t see this prohibition. Where is it written? Is it the prohibition of theft or not? What prohibition is it? From which verse? Is one liable to lashes for it? Or something else?