What is the ruling on killing geckos (lizards), and are there authentic hadiths concerning it?

The Prophet commanded the killing of geckos and called them "little evildoers" (fuwaysiqan) because a gecko used to blow fire upon Abraham (peace be upon him). It is narrated that whoever kills a gecko with the first blow will receive a hundred good deeds, and whoever kills it with the second or third blow will receive fewer good deeds.