The Qu’ran doesn’t label dogs as untouchable (in fact, there’s quite a nice vignette of the Prophet Muhammad setting a guard for a dog with a litter of puppies).
According to Mohammed Hanif, writing in The New York Times, “[m]ost of Muslims’ dog hate comes to us via the Hadith.” Which makes one wonder (yet again) about the veracity of the corpus of sayings of the Prophet as reported by his Companions…and repeated through the ages (sort of like a centuries-long game of ‘telephone’).
Check out what Hanif has to say here.