I have read a bit about Gauss, who was well known for being careful in only publishing work he had perfected (or in his own words "few, but ripe"). What is interesting to me about Gauss though is that all accounts of his students and contemporaries essentially make him appear flawless. Dedekind's recollections of how whenever Gauss wrote out an argument he used exactly the amount of space he had available, etc. In Disquistiones Arithmeticae, Gauss for example points out the flaws and shortcomings of other famous mathematicians such as Euler, who some might rank close to Gauss.
So I am curious if there is a single recorded instance of Gauss ever having made a mathematical error.