The Fourth Ecumenical Council.  The Council of Chalcedon 21Canon VI.

Neither presbyter, deacon, nor any of the ecclesiastical order shall be ordained at large, nor unless the person ordained is particularly appointed to a church in a city or village, or to a martyry, or to a monastery. And if any have been ordained without a charge, the holy Synod decrees, to the reproach of the ordainer, that such an ordination shall be inoperative, and that such shall nowhere be suffered to officiate.