Resurrection by Leo Tolstoy

When they had passed the bachelors' room the sergeant who accompanied Nekhlúdoff left him, promising to come for him before the inspection would take place. As soon as the sergeant was gone a prisoner, quickly stepping with his bare feet and holding up the chains, came close up to Nekhlúdoff, enveloping him in the strong, acid smell of perspiration, and said in a mysterious whisper: "Help the lad, sir; he's got into an awful mess. Been drinking. Today he's given his name as Karmánoff at the inspection. Take his part, sir. We dare not, or they'll kill us," and looking uneasily round he turned away.

This is what had happened. The criminal Karmánoff had persuaded a young fellow who resembled him in appearance and was sentenced to exile to change names with him and go to the mines instead of him, while he only went to exile. Nekhlúdoff knew all this. Some convict had told him about this exchange the week before. He nodded as a sign that he understood and would do what was in his power, and continued his way without looking round.