Umm Shurayk relates that Allah’s Messenger peace be upon him ordered the wazagh to be killed, and he said: “It had blown on (the fire) of Abraham (peace be upon him).” [Sahîh al-Bukhârî (3359)]
The animal in question is a type of house gecko known in Arabic by the name wazagh. It is a common household pest in the Middle East that lives on the walls and in the crevices of people’s homes.
The instruction to kill the wazagh is no different than the instruction to kill the scorpion, the poisonous snake, the mouse, and the feral dog that attacks people.
There is an authentic hadîth that mentions the killing of the “five serious pests” in both normal lands as well as in the sacred precincts, and they are the snake, the scorpion, the feral dog, the mouse, and the kite (a type of bird of prey). The reason these animals may be killed is because they are pests that cause harm to people when they make their homes in places of human habitation. These pests were known in Arabia to cause harm.
The instruction to kill the wazagh is for the same reason – it is a pest that poses harm to people. If a wazagh comes in contact with the skin, it can sometimes induce serious irritation. For this reason, it is also known to Arabs as sâmm abras (literally, “the leprosy venom”).
It is not killed because of its blowing on the fire kindled for Abraham (peace be upon him). When Prophet Muhammad (peace be upon him) informed us that the wazagh blew upon the fire of Abraham (peace be upon him) to help fan the flames, he was merely depicting the distastefulness of the animal and the extent of its harmfulness. He was merely characterizing this species as an unpleasant one.
As for your question of what sin is upon the wazaghs of today so that all of them should be punished for the act of a single wazagh of antiquity, we say that this is not the case at all. We are instructed to kill the wazagh simply because it is a harmful household pest, since it irritates people’s skin and it also forces people to discard the food that it comes in contact with. This is the reason why it should be killed, to preserve the comfort and cleanliness of places of human habitation, and not because of any sin of some past wazagh.
And Allah knows best.