Source, in full
Words said when Armstrong first stepped onto the Moon (20 July 1969) One Small Step, transcript of Apollo 11 Moon landing. In the actual sound recordings he apparently fails to say "a" before "man" and says: "That's one small step for man, one giant leap for mankind." This was generally considered by many to simply be an error of omission on his part. Armstrong long insisted he did say "a man" but that it was inaudible. Prior to new evidence supporting his claim, he stated a preference for the "a" to appear in parentheses when the quote is written. The debate continues on the matter, as "Armstrong's 'poetic' slip on Moon" at BBC News (3 June 2009) reports that more recent analysis by linguist John Olsson and author Chris Riley with higher quality recordings indicates that he did not say "a".