Praise be to Allah.
Keeping a dog is haraam, unless it is a dog for farming or hunting, or a sheep dog. It is haraam to keep any kind of dog apart from these, because that takes away one qeeraat of reward from its owner each day. According to another report, it takes away two qeeraats. If it is kept for a purpose which is allowed, if it licks a vessel or anything else, it must be purified, by washing it seven times, one of which must be with soil. This is if one is certain that it has licked it. In cases where there is doubt, it is not obligatory to wash it if we are not certain, because the basic principle is that things are pure.