Sahih Muslim , Book 26, Hadith 5566 (USC-MSA) ⓘ
Abu Huraira reported Allah's Messenger as saying (that he who kills a gecko) with the first stroke there are seventy rewards for him.
وَحَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ، حَدَّثَنَا إِسْمَاعِيلُ يَعْنِي ابْنَ زَكَرِيَّاءَ، عَنْ سُهَيْلٍ، حَدَّثَتْنِي أُخْتِي، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ " فِي أَوَّلِ ضَرْبَةٍ سَبْعِينَ حَسَنَةً " .
also referenced under: Book 39, Hadith 199 (In-Book) & Hadith 2240 (Reference)