Question: If a dog or any other animal sniffs your clothes or leaves it's saliva on them do your clothes become najis? If so is it correct that you have to change your clothes before offering Salah.
Answer: The saliva of dogs and beasts of prey are all najis, and it must be removed if the spot is a dirham in size or larger. For more details see articles under purification at this site.
... and Allaah knows best.
