Who said Its a far far better thing I do than I have ever done before?

It is a quote from The Tale of Two Cities by Charles Dickens. The original sentence was It is a far, far better thing that I do, than I have ever done; it is a far, far better rest that I go to, than I have ever known. The man speaking has volunteered to take the place of a man condemned to die. the line spoken was from lawyer Sydney Carton taking the place of the nephew of the Marquis Evrémonde