Sahih Muslim | Book 26 | Hadith Number 5564

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: He who killed a gecko with the first stroke for him is such and such a reward, and he who killed it with a second stroke for him is such and such reward less than the first one, and he who killed it with the third stroke for him is such and such a reward less than the second one.