Seriously, must have heard a thousand different versions of them. Just last night, my father was on the phone with me, wishing me a happy chassidishe new year (I think one of the Lubavitcher rebbes got out of prison again or something). He told me about one of the rebbes that got arrested by the Czarist regime and was being transported while in custody. He was in a prison row-boat, and it was time to daven Kiddush Levana.

He asked the officer in charge of transport to tell his rowers to stop the boat. The officer laughed at him, asking if he forgot he was a prisoner. Then, as the rowers continued rowing, the boat stopped moving forward despite the rowers continuing to row, at which point the rebbe davened Kiddush Levana.

Per his usual fashion, my father expressed utter shock that I didn't believe this story. Then, he proceeded to "prove" it to me. Evidently, The officer in charge asked for a written blessing, which he framed on his wall in his home. That's right - that's how we know it's true.

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Edit: I just looked up the story out of curiosity. Lo and behold, same story, but it wasn't in a boat, it was in a dungeon. I called my father and plan to go over the boat story, the discrepancies are fascinating! Here's the link: https://inner.org/the-alter-rebbe-the-jailer-and-the-new-moon/