Tell your master that if there were as many devils at Worms as tiles on its roofs, I would enter.
Source, in full
Psalm. Ein feste Burg ist unser Gott (translated by Frederic H. Hedge), Reported in Bartlett's Familiar Quotations, 10th ed. (1919). "On the 16th of April, 1521, Luther entered the imperial city [of Worms]... On his approach… the Elector's chancellor entreated him, in the name of his master, not to enter a town where his death was decided. The answer which Luther returned was simply this". Bunsen, Life of Luther