Sahih Muslim Book - 1, Hadith - 335

حَدَّثَنَا يَحْيَى بْنُ أَيُّوبَ وَقُتَيْبَةُ وَابْنُ حُجْرٍ قَالُوا حَدَّثَنَا إِسْمَاعِيلُ وَهُوَ ابْنُ جَعْفَرٍ عَنْ الْعَلَاءِ عَنْ أَبِيهِ عَنْ أَبِي هُرَيْرَةَ عَنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ قَالَ اللَّهُ عَزَّ وَجَلَّ إِذَا هَمَّ عَبْدِي بِحَسَنَةٍ وَلَمْ يَعْمَلْهَا كَتَبْتُهَا لَهُ حَسَنَةً فَإِنْ عَمِلَهَا كَتَبْتُهَا عَشْرَ حَسَنَاتٍ إِلَى سَبْعِ مِائَةِ ضِعْفٍ وَإِذَا هَمَّ بِسَيِّئَةٍ وَلَمْ يَعْمَلْهَا لَمْ أَكْتُبْهَا عَلَيْهِ فَإِنْ عَمِلَهَا كَتَبْتُهَا سَيِّئَةً وَاحِدَةً.

It was narrated from Abu Hurairah that the Messenger of Allah (s.a.w) said: "Allah, the Mighty and Sublime, said: 'If My slave thinks of doing a good deed and does not do it, I will write it down as one good deed. If he does it, I will write it down for him between ten and seven-hundred fold. If he thinks of doing a bad deed and does not do it, I will not write it down, and if he does it, I will write it down as one bad deed."'