The Messenger of Allah (ﷺ) said, "He who kills a chameleon at the first blow, such and such number of good deeds will be awarded to him; whoever kills it at the second blow, such and such number of merits will be recorded for him. And if he kills it at the third blow, he will get such and such merits."

Another narration is: The Messenger of Allah (ﷺ) said, "If anyone kills a chameleon with the first blow, a hundred good deeds will be recorded for him; less than that will be recorded for him if he kills it at the second blow, and still less rewards will be recorded for him if he kills it at the third blow."

[Muslim].