OnGUI behind UI?
How to make OnGUI() Text appear behind Canvas/UI?
Comment
I don't know why would you want to do something like that, but maybe this answered question helps: http://answers.unity3d.com/questions/774008/how-to-place-a-sprite-above-a-guidrawtexture.html
Please, next time do a $$anonymous$$imium research before asking new questions, thats almost the first result when looking for "unity legacy GUI behind uGUI" in Google. And if the answers you found don't work, explain what you've already tried in the body of the question.