Does vomiting invalidate the fast if it is unintentional, and does it break the fast if it returns to the throat?

There is no disagreement among scholars that intentional vomiting invalidates the fast. However, if one is overcome by vomiting, it does not invalidate their fast. The proof for this is the Prophet's (peace be upon him) saying: "Whoever is overcome by vomit, there is no making up for the fast upon him, but whoever vomits intentionally, let him make up for it."

And if some of the vomit returns to the stomach unintentionally, then his fast is valid.