It is narrated from Sayyiduna Abu Dharr (may Allah be pleased with him), he says: I said, "O Messenger of Allah! Advise me." The Prophet (peace and blessings be upon him) said: "When you commit a bad deed, then follow it up with a good deed, so that it may erase the effect of that bad deed." I said, "O Messenger of Allah! Is 'La ilaha illallah' (There is no god but Allah) also a good deed?" The Prophet (peace and blessings be upon him) said: "It is the most virtuous of good deeds."