Sunan Abi Dawud, Book 41, Hadith 5243 (USC-MSA)

Narrated AbuHurayrah: The Prophet 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.

حَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ الْبَزَّازُ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ زَكَرِيَّا، عَنْ سُهَيْلٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ قَتَلَ وَزَغَةً فِي أَوَّلِ ضَرْبَةٍ فَلَهُ كَذَا وَكَذَا حَسَنَةً وَمَنْ قَتَلَهَا فِي الضَّرْبَةِ الثَّانِيَةِ فَلَهُ كَذَا وَكَذَا حَسَنَةً أَدْنَى مِنَ الأَوَّلِ وَمَنْ قَتَلَهَا فِي الضَّرْبَةِ الثَّالِثَةِ فَلَهُ كَذَا وَكَذَا حَسَنَةً أَدْنَى مِنَ الثَّانِيَةِ ‏" ‏ ‏.‏

sunnah.com