"Five animals that are malicious and permissible to kill, whether in the Haram or without;
the rabid/vicious dog, [Scholars have included all types of predatory animals such as lions, wolves, leopards etc… ]
Al Haafidh ibn Hajar stated: The dog has the qualities of both the tame and wild animal, it is as if it is made up of both. It has benefits such as guarding and hunting, it can track a scent and follow tracks, it sleeps lightly, it is loving and has the ability to learn – which other animals don’t. It is said that the first person to use a dog for guarding is Nooh – ‘Alayhi as Salaam'
the crow, [in some narrations; the crow that is black and white.]
and the rat.
At Turbeeshtee stated: "Each one of these is Faasiq, and what is meant is their malice and the abundant harm they cause."
"They are to be killed whether in or out of the Haram…"
Meaning whether a person is in a state of Ihraam or not, [other scholars explained it as whether you are inside the borders of the Haram or not].
At Turbeeshtee stated: "These five were specified due to the harm they cause and the venom that some of them carry, as Allah has knowledge of their harms. Or that they cause more harm to mankind than good, and are quick to destroy things. Mankind is also unable to repel them and be safe from them, because some of them can fly and therefore cannot be caught. Others hide in holes beneath the ground; waiting for an opportunity to presents itself, it would then rush to cause harm, and if it feels it is being pursued, it remains motionless in its hiding place. Others cannot be prevented from harm, rather they continuously attack like an enemy. They may attack one who is trying to stay away from them just as readily as they would attack one who is pursuing them. Likewise they have the ability to attack mankind because they live amongst them, in contrast to other wild animals who stay away from towns and cities and remain in their own environments, which enables mankind to take due precaution of them…
The Hadeeth was collected by both Al Bukhaaree and Muslim.