Musnad Abu Ya'la al-Mawsili 117:94

Abu al-Rabi' narrated to us, al-Harith narrated to us, from Thabit, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to a man, "O so-and-so, did you do such and such?" He said, "No, by Allah, besides whom there is no god, I did not do it." And the Messenger of Allah knew that he had done it. So he said to him, "Allah has expiated your lie by your affirmation of 'There is no god but Allah'."