Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Fourth Ecumenical Council.  The Council of Chalcedon.: Canon XIII

Canon XIII.

Strange and unknown clergymen without letters commendatory from their own Bishop, are absolutely prohibited from officiating in another city.

Notes.

Ancient Epitome of Canon XIII.

No cleric shall be received to communion in another city without a letter commendatory.

“Unknown clergymen.”  I have here followed the reading of the Greek commentators.  But the translators of the Prisca, and Dionysius, and Isidore must have all read ἀναγνώστας (i.e., Readers) instead of ἀγνώστους.  Justellus, Hervetus, and Beveridge, as also Johnson and Hammond, follow the reading of the text.  Hefele suggests that if “Readers” is the correct reading perhaps it means, “all clergymen even readers.”