Musnad Abu Ya'la al-Mawsili 117:177

Shayban narrated to us, Hammad narrated to us, from Thabit, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever intends a good deed but does not perform it, a good deed is recorded for him. If he performs it, ten are recorded for him. And whoever intends a bad deed but does not perform it, nothing is recorded against him. If he performs it, one bad deed is recorded against him."