The Legend of the White Snake, also known as Madame White Snake, is a Chinese legend which existed in oral tradition long before any written compilation.
Annnnnd this is why Wikipedia isn't very reliable right now. I mean, it's not that it's impossible for oral tradition to be much older than the written one, it's just that "long before" isn't a concept which is meaningful in an encyclopaedia (1 month? 1 year? 10 centuries?), no reason is listed for this belief, no year is given for the first occurrence in written form (giving instead printed form, which is not the same) and no source is given.
If any of you ever has to write a paper, please do a better job than this
Also, on second thought, I think I read that story as a kid.