Council of Chalcedon
Council of Chalcedon, Canon XIII
Definition of faith and received canons; reception qualifications retained; not the full proceedings
Canon XIII
Strange and unknown clergymen without letters commendatory from their own Bishop, are absolutely prohibited from officiating in another city.
Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.
Source: Council of Chalcedon (CCEL)