Musnad Abu Ya'la al-Mawsili 159:34

Abu Khaythama narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, from the Prophet (peace be upon him), who said: Allah said: "If My servant intends a good deed, then write it down for him as one good deed. If he performs it, then write it down for him as ten times its like. If he intends a bad deed, then do not write it down. If he performs it, then write it down as one bad deed. And if he leaves it, then write it down as a good deed."