Musnad Ahmad 30:3233

Bahz narrated to us, Hammam narrated to us, he said: Qatadah narrated to us, from Zurarah ibn Awfa, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah, the Almighty and Majestic, has pardoned for my nation everything that their souls whisper to them, as long as they do not speak of it or act upon it."