The saliva, urine, and sweat of a dog are considered najis (impure or unclean) according to Shafi'i and Hanbali scholars.
In Islamic jurisprudence, najasah refers to ritual impurity. Contact with something that is najis requires purification before performing ritual acts like prayer. Regarding dogs, the specific aspects considered impure are their bodily fluids. The transmission of impurity occurs when a wet dog or a wet surface that has been in contact with a dog comes into contact with a clean, wet surface. The point of contact then also becomes impure.
Essentially, this means if a dry dog touches a dry surface, there is no transmission of najasah. However, if either the dog or the surface is wet, the point of contact becomes impure.
