Sahih Muslim 2240 a
Abu Huraira reported Allah's Messenger (ﷺ) 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.
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، 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 لِدُونِ الأُولَى وَإِنْ قَتَلَهَا
 فِي الضَّرْبَةِ الثَّالِثَةِ فَلَهُ كَذَا وَكَذَا حَسَنَةً لِدُونِ الثَّانِيَةِ ‏"‏ ‏.‏