Who asked Captain Ahab if Moby Dick had taken off his leg?

At the beginning of Chapter 100 of Moby Dick, the Pequod pulls alongside an English ship, the Samuel Enderby. Naturally, Ahab's keen to find out from the captain of the other ship whether he's seen the great white whale. As luck would have it—for Ahab, that is, not the captain—the captain of the Samuel Enderby has indeed encountered Moby Dick; he lost his arm to the white whale and now sports an artificial arm made out of ivory.
He points his ivory limb east toward the horizon and tells Ahab that that was where he saw Moby Dick the previous season. It was during this unfortunate encounter that the whale made off with the captain's arm. When the captain sees Ahab's peg leg, he asks him if that, too, was caused by Moby Dick. Ahab doesn't give him a straight answer; instead, he asks the captain to spin him a yarn, to tell him what happened that fateful day when he encountered the fearsome Moby Dick.