Council of Ephesus, Canon III

If any of the city or country clergy have been inhibited by Nestorius or his followers from the exercise of the priesthood, on account of their orthodoxy, we have declared it just that these should be restored to their proper rank.  And in general we forbid all the clergy who adhere to the Orthodox and Ecumenical Synod in any way to submit to the bishops who have already apostatized or shall hereafter apostatize.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.