37. On Prohibition and Permission (Al-Hazr wa 'l-Ibahah)
Abu Ja‘far says, concerning prohibition and permission, that "Everything is permitted . . ."ash-Shaykh al-Mufid says: Things according to the dictates of reason fall into two categories; the first, those which are conceived as prohibited by reason, these are the things which reason abhors and admonishes against, such as injustice, foolishness and vanity. The second are those which are not defined by reason as either forbidden or lawful but only by textual proof (sam‘).
This group includes deeds, the performance of which may corrupt on one occasion and be beneficial on another, and they are restricted to the rulings of canon law, which have suffered abrogation and amendment. Since, however the religious law is settled once and for all, the general decision is that: Everything that is not prohibited by nass (i.e., the specific ordinances of religion) is permitted, because the religious canon has laid down the limits of the law, and distinguished finally what is prohibited, so it follows logically that what lies outside their scope is permitted.