As far as I know, there is no such instance...but...as far as the entire corpus of Classical Latin goes, for me, that's not saying much.
However, as to your second question, I can at least point out what happened with French, and it comes from a process of grammaticalization. Note
, the following is not my own example. It comes from a lecture by John McWhorter out of UC Berkeley.
In old French, you could make a negative out of a sentence by just throwing in "ne." Like "il ne marche" (he does not walk) or "je ne sais" (I don't know).
To stengthen or emphasize the negative, the medieval French did what we often do in modern English: "I can't eat another bite
," or "I can't go any farther
." "Pas," aside from being part of the negative construction used in French today, also means "a step." So, when negating a sentence such as "il ne marche," and emphasizing the negative, you would say "il ne marche pas," or "he doesn't walk a step." This happened with other phrases as well..."he won't eat a bit," "she won't drink a drop," etc.
Eventually, "pas" became part of the negative construction, with the original, pure meaning sidelined and its original force weakened until there was no difference between "il ne marche" and "il ne marche pas." To quote McWhorter: "In this situation, 'pas' no longer seemed to mean 'step' at all. By the 1500s, 'pas' started to seem as if it were a new way of saying 'not' along with 'ne.' And, eventually, it was. This meant you could use it with any verb, even ones that had nothing to do with walking."
Hope this helps a little
(emphasizing the positive