Nicæa I: canon XV

On account of the great disturbance and the factions which are caused, it is decreed that the custom, if it is found to exist in some parts contrary to the canon, shall be totally suppressed, so that neither bishops nor presbyters nor deacons shall transfer from city to city. If after this decision of this holy and great synod anyone shall attempt such a thing, or shall lend himself to such a proceeding, the arrangement shall be totally annulled, and he shall be restored to the church of which he was ordained bishop or presbyter or deacon.