"Luther's strength lay in the way he laid the burden of the Reformation upon the Lord. Continually in prayer he pleaded, 'Lord, this is Thy cause, not mine. Therefore, do thine own work; for if this gospel do not prosper, it will not be Luther alone who will be a loser, but Thine own name will be dishonored.'"(Source: Spurgeon's Sermon Notes)
Recommended reading:
You can also listen to an audio recording of The Forgotten Spurgeon on Sermonaudio.com: