Martin Luther:

If I profess with the loudest voice and clearest exposition every portion of the Word of God except precisely that little point which the world and the devil are at that moment attacking, I am not confessing Christ, however boldly I may be professing Him. Where the battle rages there the loyalty of the soldier is proved; and to be steady on all the battle front besides, is mere flight and disgrace if he flinches at that point.

But did he ever really write that? Denny Burk has looked, and thus far cannot find the original. Can anyone provide the original quote, beyond the one that Burk has provided?