Abu Hurairah (RA) narrates that some of the Sahãbah (Ra) came to Nabí (saw) and asked him: We find that, in our hearts, arise such thoughts that we would be ashamed to talk of them. He said: Well, do you indeed feel like that? We said: Yes. He replied: That is pure Ímãn. (Muslim)

Note: This means that when these thoughts instigate you and far from believing in them, you do not even want to utter them. Then indeed this is the sign of perfect Ímãn.