well there is a book by Janet and Stewart Farrar called The Witches Bible, it's basically a beginners guide to witchcraft. i haven't read it in a while, but i own a copy, it's not bad. is it necessary to being a witch, no.
if you mean a Grimoire or Book of Shadows, you make that yourself, it's more of a recipe book than a bible, and it doesn't determine if you're a witch or not, it's used as a reference. if you call yourself a witch, then you're a witch really. to be a witch, to most people, you are trying to learn, or you cast spells, or you follow a more earth conscious path, it doesn't mean you have a book.