While it is good to use illustrations to explain apply, argue or celebrate a truth. I was confronted with the necessary practice of looking to Scripture for my illustrations first. I have heard the advise of using scripture as the only source of sermon illustrations, which I thought was not biblical,, but I am considering this arguement from "Soul Preaching" that since the Bible is the preeminent authority, we should seek illustrations from the Bible first. This is not to say that we cannot use other sources, but recognizes that all other sources of authority (history, experience, science, tradition, etc.) are lesser authorities.
See what you think in reading Scriptures as Sermon Illustration Resource | Soul Preaching Ministries