What is the reason for the dog being with the People of the Cave, even though a dog is impure?

The Companions of the Cave were youths whom Allah guided to faith. They knew their Lord and rejected their people's worship of idols. The dog with them was a hunting or guard dog, which is the usual practice for dogs to lie at the door to protect their owners. Their blessings extended to their dog, so it attained the same sleep they did. The presence of the dog with them does not indicate the permissibility of keeping dogs in our Shari'ah except for hunting or guarding livestock and crops. This is how the action of the Companions of the Cave is interpreted, as they were people of goodness. This was the law of those before us, and it is not necessarily a law for us except in what our Shari'ah has permitted.