Musnad Ahmad 30:3006

Yahya narrated to us, from Ibn Abi Arubah, who said: Qatadah narrated to us, from Zurarah, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, Allah has pardoned for my nation what their souls whisper to them, as long as they do not act upon it or speak of it."