Having ascertained the places which it frequents and passes, they stop the way to them with mud, and then rousing it, drive it towards the spot, and as soon as the ermine comes to the mud it halts, and allows itself to be taken captive rather than pass through the mire, and spoil and sully its whiteness, which it values more than life and liberty.
There are no more uses of "sully" in the book.
Show samples from other sources
And though in near time we did sleep together (with a genuinely pleasing, if sober, conviviality), I came to think of that first interlude with a somewhat sorrowful fondness, for I saw that our days together were perhaps sullied from the very beginning and all the way through, right up to the last.
Chang-rae Lee -- A Gesture Life
Maybe I would waste my time on skills I didn’t care about—like sword fighting or badminton—but I would not sully the memory of my once-perfect music and archery.