'Know that wrongdoing is of three types: the wrongdoing that is unforgivable, the wrongdoing that cannot be left unaccounted, and the wrongdoing that is forgivable and unquestioned. The wrong that is unforgivable is association of anything with Allah ...the wrong that is forgivable is when the servant is unjust to himself and wrongs himself with regard to his faults, and the wrong that cannot be left unaccounted is the wrong that people do unto each other.'