Musnad Ahmad 2000

Ibn "Abbas narrated that the Prophet (ﷺ) said: “if [a person] thinks of doing a good deed then does it, it will be recorded as ten, and if he does not do it, it will be recorded as one hasanah. If he thinks of doing a bad deed and does it, it will be recorded as one sayyi’ah, and if he does not do it, it will be recorded as one hasanah.”