Abu Dawud Book 36, Hadith Number 5243.
Chapter : Not known.
Narated By AbuHurayrah : The Prophet (PBUH) said: If anyone kills a gecko with the first blow, such and such number of good deeds will be recorded for him, if he kills it with the second blow, such and such number of good deeds will be recorded for him less than the former; and if he kills it with the third blow, such and such number of good deeds will be recorded for him, less than the former.