There are two sacristy prayers of Luther that circulate. Here is one:

Lord God, You have appointed me as a Bishop and Pastor in Your Church, but you see how unsuited I am to meet so great and difficult a task. If I had lacked Your help, I would have ruined everything long ago. Therefore, I call upon You: I wish to devote my mouth and my heart to you; I shall teach the people. I myself will learn and ponder diligently upon Your Word. Use me as Your instrument — but do not forsake me, for if ever I should be on my own, I would easily wreck it all.