[Categories of oppression :] Know that injustice is of three kinds — one, the injustice that will not be forgiven, another, that will not be left unquestioned, and another that will be forgiven without being questioned. The injustice that will not be forgiven is duality of Allāh. Allāh has said: Verily Allāh forgiveth not that (anything) be associated with Him . . . (Qur’ān, 4:48, 116). The injustice that will be forgiven is the injustice a man does to himself by committing small sins; and the injustice that will not be left unquestioned is the injustice of men against other men. The retribution in such a case is severe. It is not wounding with knives, nor striking with whips, but it is so severe that all these things are small against it. You should therefore avoid change in the matter of Allāh’s religion for your unity in respect of a right which you dislike is better than your scattering away in respect of a wrong that you like. Certainly, Allāh the Glorified has not given any person, whether among the dead or among those who survive, any good from separation.