Musnad Ahmed: Hadith 3379

The Messenger of Allah (ﷺ) said, relating from his Lord, may He be glorified and exalted: "Allah decreed good deeds and bad deeds, then He explained that. Whoever thinks of doing a good deed then does not do it, Allah will write it down for him as one complete good deed. If he thinks of doing a good deed and then does it, Allah (may He be glorified and exalted) will write it down for him between ten and seven hundred fold, or many more. If he thinks of doing a bad deed then he does not do it. Allah will write it down for him as one complete good deed, and if he thinks of it then does it, Allah will write it down for him as one bad deed.”