Ahadith On Keeping Dogs
We don’t know the real cause of these narrations which discourage keeping dogs as pet, but we know that the cause must have been a reasonable one for example: there might contagious disease in the dogs during that time. However, this can’t be a permanent or general directive. The prophet as head of the sate issued such ordinance time to time for example once he encouraged Muslims to kill lizards and they will get reward. since he was the prophet, so for every good act, he could have announced a specific reward as he was in communication with God.