Sayyiduna Ali (may Allah be pleased with him) says: We were waiting for prayer in the mosque with the Prophet (peace and blessings be upon him) when a man stood up and said: A sin has been committed by me. The Prophet (peace and blessings be upon him) turned away from him. Then, when the Prophet (peace and blessings be upon him) had finished speaking, that person stood up again and repeated his statement. So the Prophet (peace and blessings be upon him) said: "Did you perform this prayer with us and make ablution for it properly?" He said: Yes! The Prophet (peace and blessings be upon him) said: "Then this has become an expiation for your sin."