I am writing a speech and I need a credibility statement. What would be an example of one?

It depends on the topic of your speech and whether you are giving credibility to yourself as the writer of the speech or giving credibility to the speech based on information derived from a credible outside source (scholarly journal, expert in field etc..). Giving credit to yourself is easy, for example if your paper is about sports, you can say that you have been an avid sports fan your whole life, keep track of key players, read sports books and have played sports and therefore you are knowledgeable on the topic and therefore your speech has credible information.