@burcidi, @alisha-- I agree with both of you. Malapropisms is one of the reasons why I read a lot. The more I read and see how things are spelled, the less room there is for mistakes.
When we use idioms that we've only heard and not read or written, we're bound to make mistakes with spellings and the use of words.
If one thinks about it though, it's so obvious that hare's breath or hair's breath isn't right. I mean hares breathe but what does that have to do with something happening or not happening by a narrow margin? A hair's breath doesn't make sense at all! It all goes down to common sense. We all have access to the internet, it takes a minute to look it up!