Sahih Muslim Book 1, Hadith Number 231.

Chapter : Allah disregards the premonition of the evil promptings of the heart so long as they do not take a firm-root.

It is narrated on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) observed: Verily the Great and Mighty Allah forgave my people the evil promptings arising in their minds, but they neither talked about them nor acted upon them.