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 LIX

Canon LIX.  (Greek lxiii.)

That clerics be not compelled to give testimony in public concerning the cognizance of their own judgment.

It should be petitioned also that they deign to decree, that if perchance any shall have been willing to plead their cause in any church according to the Apostolic law imposed upon the Churches, and it happens that the decision of the clergy does not satisfy one of the parties, it be not lawful to summon that clergyman who had been cognitor or present, 459 into judgment as a witness, and that no person attached to any ecclesiastic be compelled to give testimony.

Notes.

Ancient Epitome of Canon LIX.

A cleric who has decided a case shall not, if it be displeasing, be summoned to a tribunal to give evidence concerning it; and no ecclesiastical person shall be forced to give testimony.

This is Canon iij. of the Synod of Carthage, June 15 (or 16). a.d. 401.

Johnson.

“According to the Apostolic law,” viz., that of St. Paul, 1 Cor. 6:1, 2, etc.  I follow the Greek scholia in rendering this canon.  In Latin cognitor is he that is solicitor, or advocate, rather than the judge who takes cognizance.

Footnotes

This must mean “who had heard the cause or been present at the hearing,” and so the Greek has it.