“Horse of Destruction”, Scene 5: Inside the Horse

On these albums

Doctor Who: The Myth MakersDonald Cotton starring William Hartnell, Maureen O’Brien & Peter Purves · 2001Soundtrack

Doctor Who: Adventures in HistoryWilliam Hartnell, Patrick Troughton with linking narration by Peter Purves & Frazer Hines · 2003Soundtrack

Doctor Who: The Lost TV Episodes - Collection OneVarious Artists · 2010

Source: MusicBrainz recording 2c79e298-525c-4fb1-98e0-c4d9c43ba901 (CC0).