It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that once the Prophet (peace and blessings be upon him) asked a person, "Did you do this act?" He replied, "O Messenger of Allah! By Him besides whom there is no deity, I did not do this act." The Prophet (peace and blessings be upon him) said, "Indeed, you did do that act, but due to the sincerity with which you said 'La ilaha illallah,' you have been forgiven."