I'll probably be downvoted into oblivion for this, but this is a per peeve of mine. Your use of the expression doesn't make sense.

The expression is highlighting that you need to observe a negative in order to determine whether a rule is true. For example, if I make the statement: "Only birds have wings", then any observation of a non-bird without wings are exceptions to the rule that proves said rule.

The observation of a bat is indeed an exception to the rule, but it does not prove it. In fact, it does the opposite. It disproves it.