It is narrated from Sayyiduna Imran bin Husayn (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "My Ummah has been pardoned for what occurs in their hearts, as long as they do not speak of it with their tongues or act upon it."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15630