1 Kings 8:36

then hear Thou in heaven, and forgive the sin of Thy servants and of Thy people Israel, that Thou teach them the good way wherein they should walk, and give rain upon Thy land which Thou hast given to Thy people for an inheritance. Because God teaches, educates, His people, tries to bring them back to the right way by means of punishments, therefore He is asked to forgive if His people acknowledge the punishment and plead for forgiveness.