Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Synods of Sardica, Carthage, Constantinople, and Carthage Under St. Cyprian, Which Canons Were Received by the Council in Trullo and Ratified by II. Nice.: Canon CXXIX

Canon CXXIX.  (Greek cxxx.)

That slaves and freedmen and all infamous persons ought not to bring accusation.

To all it seemed good that no slaves or freedmen, properly so called, be admitted to accusation nor any of those who by the public laws are debarred from bringing accusation in criminal proceedings.  This also is the case with all those who have the stain of infamy, that is actors, and persons subject to turpitudes, also heretics, or heathen, or Jews; but even all those to whom the right of bringing accusation is denied, are not forbidden to bring accusation in their own suits.

Notes.

Ancient Epitome of Canon CXXIX.

A slave, and a freedman, and he who before was accused of any of these crimes on account of which he is not admitted in court, and a player, and a heathen, and a heretic, and a Jew.

[There is no verb to finish the sentence.  However, this is intended as a continuation of the epitome of the former canon, the words to be supplied being “are not to give witness.”]

Johnson.

See Can., Const., 6.